DEFINITION csuba_drop_abbr_rev()
TYPE =
       i:nat
         .c1:C
           .d1:C
             .u1:T
               .drop i O c1 (CHead d1 (Bind Abbr) u1)
                 g:G
                      .c2:C
                        .csuba g c2 c1
                          (or3
                               ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                               ex4_3
                                 C
                                 T
                                 A
                                 λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abst) u2)
                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                               ex2_2 C T λd2:C.λu2:T.drop i O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
BODY =
       assume inat
          we proceed by induction on i to prove 
             c1:C
               .d1:C
                 .u1:T
                   .drop i O c1 (CHead d1 (Bind Abbr) u1)
                     g:G
                          .c2:C
                            .csuba g c2 c1
                              (or3
                                   ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                   ex4_3
                                     C
                                     T
                                     A
                                     λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abst) u2)
                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                   ex2_2 C T λd2:C.λu2:T.drop i O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
             case O : 
                the thesis becomes 
                c1:C
                  .d1:C
                    .u1:T
                      .drop O O c1 (CHead d1 (Bind Abbr) u1)
                        g:G
                             .c2:C
                               .csuba g c2 c1
                                 (or3
                                      ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                      ex4_3
                                        C
                                        T
                                        A
                                        λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                      ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                    assume c1C
                    assume d1C
                    assume u1T
                    suppose Hdrop O O c1 (CHead d1 (Bind Abbr) u1)
                    assume gG
                    assume c2C
                    suppose H0csuba g c2 c1
                      (H1
                         by (drop_gen_refl . . H)
                         we proved eq C c1 (CHead d1 (Bind Abbr) u1)
                         we proceed by induction on the previous result to prove csuba g c2 (CHead d1 (Bind Abbr) u1)
                            case refl_equal : 
                               the thesis becomes the hypothesis H0
csuba g c2 (CHead d1 (Bind Abbr) u1)
                      end of H1
                      (H_x
                         by (csuba_gen_abbr_rev . . . . H1)

                            or3
                              ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                              ex4_3
                                C
                                T
                                A
                                λd2:C.λu2:T.λ:A.eq C c2 (CHead d2 (Bind Abst) u2)
                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                λ:C.λ:T.λa:A.arity g d1 u1 a
                              ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                      end of H_x
                      (H2consider H_x
                      we proceed by induction on H2 to prove 
                         or3
                           ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                           ex4_3
                             C
                             T
                             A
                             λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                             λd2:C.λ:T.λ:A.csuba g d2 d1
                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                             λ:C.λ:T.λa:A.arity g d1 u1 a
                           ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                         case or3_intro0 : H3:ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                            the thesis becomes 
                            or3
                              ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                              ex4_3
                                C
                                T
                                A
                                λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                λ:C.λ:T.λa:A.arity g d1 u1 a
                              ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                               we proceed by induction on H3 to prove 
                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                  case ex_intro2 : x:C H4:eq C c2 (CHead x (Bind Abbr) u1) H5:csuba g x d1 
                                     the thesis becomes 
                                     or3
                                       ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                        by (drop_refl .)
                                        we proved drop O O (CHead x (Bind Abbr) u1) (CHead x (Bind Abbr) u1)
                                        by (ex_intro2 . . . . previous H5)
                                        we proved 
                                           ex2
                                             C
                                             λd2:C.drop O O (CHead x (Bind Abbr) u1) (CHead d2 (Bind Abbr) u1)
                                             λd2:C.csuba g d2 d1
                                        by (or3_intro0 . . . previous)
                                        we proved 
                                           or3
                                             ex2
                                               C
                                               λd2:C.drop O O (CHead x (Bind Abbr) u1) (CHead d2 (Bind Abbr) u1)
                                               λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O (CHead x (Bind Abbr) u1) (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2
                                               C
                                               T
                                               λd2:C.λu2:T.drop O O (CHead x (Bind Abbr) u1) (CHead d2 (Bind Void) u2)
                                               λd2:C.λ:T.csuba g d2 d1
                                        by (eq_ind_r . . . previous . H4)

                                           or3
                                             ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                         case or3_intro1 : H3:ex4_3 C T A λd2:C.λu2:T.λ:A.eq C c2 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                            the thesis becomes 
                            or3
                              ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                              ex4_3
                                C
                                T
                                A
                                λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                λ:C.λ:T.λa:A.arity g d1 u1 a
                              ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                               we proceed by induction on H3 to prove 
                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                  case ex4_3_intro : x0:C x1:T x2:A H4:eq C c2 (CHead x0 (Bind Abst) x1) H5:csuba g x0 d1 H6:arity g x0 x1 (asucc g x2) H7:arity g d1 u1 x2 
                                     the thesis becomes 
                                     or3
                                       ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                        by (drop_refl .)
                                        we proved drop O O (CHead x0 (Bind Abst) x1) (CHead x0 (Bind Abst) x1)
                                        by (ex4_3_intro . . . . . . . . . . previous H5 H6 H7)
                                        we proved 
                                           ex4_3
                                             C
                                             T
                                             A
                                             λd2:C.λu2:T.λ:A.drop O O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                        by (or3_intro1 . . . previous)
                                        we proved 
                                           or3
                                             ex2
                                               C
                                               λd2:C.drop O O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                               λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2
                                               C
                                               T
                                               λd2:C.λu2:T.drop O O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                               λd2:C.λ:T.csuba g d2 d1
                                        by (eq_ind_r . . . previous . H4)

                                           or3
                                             ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                         case or3_intro2 : H3:ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                            the thesis becomes 
                            or3
                              ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                              ex4_3
                                C
                                T
                                A
                                λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                λ:C.λ:T.λa:A.arity g d1 u1 a
                              ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                               we proceed by induction on H3 to prove 
                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                  case ex2_2_intro : x0:C x1:T H4:eq C c2 (CHead x0 (Bind Void) x1) H5:csuba g x0 d1 
                                     the thesis becomes 
                                     or3
                                       ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                        by (drop_refl .)
                                        we proved drop O O (CHead x0 (Bind Void) x1) (CHead x0 (Bind Void) x1)
                                        by (ex2_2_intro . . . . . . previous H5)
                                        we proved 
                                           ex2_2
                                             C
                                             T
                                             λd2:C.λu2:T.drop O O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                             λd2:C.λ:T.csuba g d2 d1
                                        by (or3_intro2 . . . previous)
                                        we proved 
                                           or3
                                             ex2
                                               C
                                               λd2:C.drop O O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                               λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2
                                               C
                                               T
                                               λd2:C.λu2:T.drop O O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                               λd2:C.λ:T.csuba g d2 d1
                                        by (eq_ind_r . . . previous . H4)

                                           or3
                                             ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                  or3
                                    ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                    ex4_3
                                      C
                                      T
                                      A
                                      λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                    ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                      we proved 
                         or3
                           ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                           ex4_3
                             C
                             T
                             A
                             λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                             λd2:C.λ:T.λ:A.csuba g d2 d1
                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                             λ:C.λ:T.λa:A.arity g d1 u1 a
                           ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                      c1:C
                        .d1:C
                          .u1:T
                            .drop O O c1 (CHead d1 (Bind Abbr) u1)
                              g:G
                                   .c2:C
                                     .csuba g c2 c1
                                       (or3
                                            ex2 C λd2:C.drop O O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                            ex4_3
                                              C
                                              T
                                              A
                                              λd2:C.λu2:T.λ:A.drop O O c2 (CHead d2 (Bind Abst) u2)
                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                            ex2_2 C T λd2:C.λu2:T.drop O O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
             case S : n:nat 
                the thesis becomes 
                c1:C
                  .d1:C
                    .u1:T
                      .drop (S n) O c1 (CHead d1 (Bind Abbr) u1)
                        g:G
                             .c2:C
                               .csuba g c2 c1
                                 (or3
                                      ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                      ex4_3
                                        C
                                        T
                                        A
                                        λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                      ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                (H) by induction hypothesis we know 
                   c1:C
                     .d1:C
                       .u1:T
                         .drop n O c1 (CHead d1 (Bind Abbr) u1)
                           g:G
                                .c2:C
                                  .csuba g c2 c1
                                    (or3
                                         ex2 C λd2:C.drop n O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                         ex4_3
                                           C
                                           T
                                           A
                                           λd2:C.λu2:T.λ:A.drop n O c2 (CHead d2 (Bind Abst) u2)
                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                         ex2_2 C T λd2:C.λu2:T.drop n O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                   assume c1C
                      we proceed by induction on c1 to prove 
                         d1:C
                           .u1:T
                             .drop (S n) O c1 (CHead d1 (Bind Abbr) u1)
                               g:G
                                    .c2:C
                                      .csuba g c2 c1
                                        (or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                         case CSort : n0:nat 
                            the thesis becomes 
                            d1:C
                              .u1:T
                                .H0:drop (S n) O (CSort n0) (CHead d1 (Bind Abbr) u1)
                                  .g:G
                                    .c2:C
                                      .csuba g c2 (CSort n0)
                                        (or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                                assume d1C
                                assume u1T
                                suppose H0drop (S n) O (CSort n0) (CHead d1 (Bind Abbr) u1)
                                assume gG
                                assume c2C
                                suppose csuba g c2 (CSort n0)
                                  by (drop_gen_sort . . . . H0)
                                  we proved 
                                     and3
                                       eq C (CHead d1 (Bind Abbr) u1) (CSort n0)
                                       eq nat (S n) O
                                       eq nat O O
                                  we proceed by induction on the previous result to prove 
                                     or3
                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                     case and3_intro : :eq C (CHead d1 (Bind Abbr) u1) (CSort n0) H3:eq nat (S n) O :eq nat O O 
                                        the thesis becomes 
                                        or3
                                          ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                          ex4_3
                                            C
                                            T
                                            A
                                            λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                            λd2:C.λ:T.λ:A.csuba g d2 d1
                                            λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                            λ:C.λ:T.λa:A.arity g d1 u1 a
                                          ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                           (H5
                                              we proceed by induction on H3 to prove <λ:nat.Prop> CASE O OF OFalse | S True
                                                 case refl_equal : 
                                                    the thesis becomes <λ:nat.Prop> CASE S n OF OFalse | S True
                                                       consider I
                                                       we proved True
<λ:nat.Prop> CASE S n OF OFalse | S True
<λ:nat.Prop> CASE O OF OFalse | S True
                                           end of H5
                                           consider H5
                                           we proved <λ:nat.Prop> CASE O OF OFalse | S True
                                           that is equivalent to False
                                           we proceed by induction on the previous result to prove 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                  we proved 
                                     or3
                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                  d1:C
                                    .u1:T
                                      .H0:drop (S n) O (CSort n0) (CHead d1 (Bind Abbr) u1)
                                        .g:G
                                          .c2:C
                                            .csuba g c2 (CSort n0)
                                              (or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                         case CHead : c:C k:K t:T 
                            the thesis becomes 
                            d1:C
                              .u1:T
                                .H1:drop (S n) O (CHead c k t) (CHead d1 (Bind Abbr) u1)
                                  .g:G
                                    .c2:C
                                      .H2:csuba g c2 (CHead c k t)
                                        .or3
                                          ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                          ex4_3
                                            C
                                            T
                                            A
                                            λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                            λd2:C.λ:T.λ:A.csuba g d2 d1
                                            λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                            λ:C.λ:T.λa:A.arity g d1 u1 a
                                          ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                            (H0) by induction hypothesis we know 
                               d1:C
                                 .u1:T
                                   .drop (S n) O c (CHead d1 (Bind Abbr) u1)
                                     g:G
                                          .c2:C
                                            .csuba g c2 c
                                              (or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
                                assume d1C
                                assume u1T
                                suppose H1drop (S n) O (CHead c k t) (CHead d1 (Bind Abbr) u1)
                                assume gG
                                assume c2C
                                suppose H2csuba g c2 (CHead c k t)
                                  by (drop_gen_drop . . . . . H1)
                                  we proved drop (r k n) O c (CHead d1 (Bind Abbr) u1)
                                     assume bB
                                      suppose H3csuba g c2 (CHead c (Bind b) t)
                                      suppose H4drop (r (Bind b) n) O c (CHead d1 (Bind Abbr) u1)
                                         suppose H5csuba g c2 (CHead c (Bind Abbr) t)
                                         suppose H6drop (r (Bind Abbr) n) O c (CHead d1 (Bind Abbr) u1)
                                           (H_x
                                              by (csuba_gen_abbr_rev . . . . H5)

                                                 or3
                                                   ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abbr) t) λd2:C.csuba g d2 c
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.eq C c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 c
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g c t a
                                                   ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 c
                                           end of H_x
                                           (H7consider H_x
                                           we proceed by induction on H7 to prove 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case or3_intro0 : H8:ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abbr) t) λd2:C.csuba g d2 c 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    we proceed by induction on H8 to prove 
                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                       case ex_intro2 : x:C H9:eq C c2 (CHead x (Bind Abbr) t) H10:csuba g x c 
                                                          the thesis becomes 
                                                          or3
                                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             (H11
                                                                consider H6
                                                                we proved drop (r (Bind Abbr) n) O c (CHead d1 (Bind Abbr) u1)
                                                                that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                                by (H . . . previous . . H10)

                                                                   or3
                                                                     ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             end of H11
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro0 : H12:ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex_intro2 : x0:C H13:drop n O x (CHead x0 (Bind Abbr) u1) H14:csuba g x0 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Abbr) u1)
                                                                               that is equivalent to drop (r (Bind Abbr) n) O x (CHead x0 (Bind Abbr) u1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abbr) t) (CHead x0 (Bind Abbr) u1)
                                                                               by (ex_intro2 . . . . previous H14)
                                                                               we proved 
                                                                                  ex2
                                                                                    C
                                                                                    λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                    λd2:C.csuba g d2 d1
                                                                               by (or3_intro0 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro1 : H12:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex4_3_intro : x0:C x1:T x2:A H13:drop n O x (CHead x0 (Bind Abst) x1) H14:csuba g x0 d1 H15:arity g x0 x1 (asucc g x2) H16:arity g d1 u1 x2 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Abst) x1)
                                                                               that is equivalent to drop (r (Bind Abbr) n) O x (CHead x0 (Bind Abst) x1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abbr) t) (CHead x0 (Bind Abst) x1)
                                                                               by (ex4_3_intro . . . . . . . . . . previous H14 H15 H16)
                                                                               we proved 
                                                                                  ex4_3
                                                                                    C
                                                                                    T
                                                                                    A
                                                                                    λd2:C
                                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                               by (or3_intro1 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro2 : H12:ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex2_2_intro : x0:C x1:T H13:drop n O x (CHead x0 (Bind Void) x1) H14:csuba g x0 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Void) x1)
                                                                               that is equivalent to drop (r (Bind Abbr) n) O x (CHead x0 (Bind Void) x1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abbr) t) (CHead x0 (Bind Void) x1)
                                                                               by (ex2_2_intro . . . . . . previous H14)
                                                                               we proved 
                                                                                  ex2_2
                                                                                    C
                                                                                    T
                                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                               by (or3_intro2 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                             we proved 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abbr) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                             by (eq_ind_r . . . previous . H9)

                                                                or3
                                                                  ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case or3_intro1 : H8:ex4_3 C T A λd2:C.λu2:T.λ:A.eq C c2 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 c λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g c t a 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    we proceed by induction on H8 to prove 
                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                       case ex4_3_intro : x0:C x1:T x2:A H9:eq C c2 (CHead x0 (Bind Abst) x1) H10:csuba g x0 c :arity g x0 x1 (asucc g x2) :arity g c t x2 
                                                          the thesis becomes 
                                                          or3
                                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             (H13
                                                                consider H6
                                                                we proved drop (r (Bind Abbr) n) O c (CHead d1 (Bind Abbr) u1)
                                                                that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                                by (H . . . previous . . H10)

                                                                   or3
                                                                     ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             end of H13
                                                             we proceed by induction on H13 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro0 : H14:ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H14 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex_intro2 : x:C H15:drop n O x0 (CHead x (Bind Abbr) u1) H16:csuba g x d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H15
                                                                               we proved drop n O x0 (CHead x (Bind Abbr) u1)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x0 (CHead x (Bind Abbr) u1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Abst) x1) (CHead x (Bind Abbr) u1)
                                                                               by (ex_intro2 . . . . previous H16)
                                                                               we proved 
                                                                                  ex2
                                                                                    C
                                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                    λd2:C.csuba g d2 d1
                                                                               by (or3_intro0 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro1 : H14:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H14 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex4_3_intro : x3:C x4:T x5:A H15:drop n O x0 (CHead x3 (Bind Abst) x4) H16:csuba g x3 d1 H17:arity g x3 x4 (asucc g x5) H18:arity g d1 u1 x5 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H15
                                                                               we proved drop n O x0 (CHead x3 (Bind Abst) x4)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x0 (CHead x3 (Bind Abst) x4)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Abst) x1) (CHead x3 (Bind Abst) x4)
                                                                               by (ex4_3_intro . . . . . . . . . . previous H16 H17 H18)
                                                                               we proved 
                                                                                  ex4_3
                                                                                    C
                                                                                    T
                                                                                    A
                                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                               by (or3_intro1 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro2 : H14:ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H14 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex2_2_intro : x3:C x4:T H15:drop n O x0 (CHead x3 (Bind Void) x4) H16:csuba g x3 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H15
                                                                               we proved drop n O x0 (CHead x3 (Bind Void) x4)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x0 (CHead x3 (Bind Void) x4)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Abst) x1) (CHead x3 (Bind Void) x4)
                                                                               by (ex2_2_intro . . . . . . previous H16)
                                                                               we proved 
                                                                                  ex2_2
                                                                                    C
                                                                                    T
                                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                               by (or3_intro2 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                             we proved 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Abst) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                             by (eq_ind_r . . . previous . H9)

                                                                or3
                                                                  ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case or3_intro2 : H8:ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 c 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    we proceed by induction on H8 to prove 
                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                       case ex2_2_intro : x0:C x1:T H9:eq C c2 (CHead x0 (Bind Void) x1) H10:csuba g x0 c 
                                                          the thesis becomes 
                                                          or3
                                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             (H11
                                                                consider H6
                                                                we proved drop (r (Bind Abbr) n) O c (CHead d1 (Bind Abbr) u1)
                                                                that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                                by (H . . . previous . . H10)

                                                                   or3
                                                                     ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             end of H11
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro0 : H12:ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex_intro2 : x:C H13:drop n O x0 (CHead x (Bind Abbr) u1) H14:csuba g x d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x (Bind Abbr) u1)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x (Bind Abbr) u1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x (Bind Abbr) u1)
                                                                               by (ex_intro2 . . . . previous H14)
                                                                               we proved 
                                                                                  ex2
                                                                                    C
                                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                    λd2:C.csuba g d2 d1
                                                                               by (or3_intro0 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro1 : H12:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex4_3_intro : x2:C x3:T x4:A H13:drop n O x0 (CHead x2 (Bind Abst) x3) H14:csuba g x2 d1 H15:arity g x2 x3 (asucc g x4) H16:arity g d1 u1 x4 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x2 (Bind Abst) x3)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x2 (Bind Abst) x3)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x2 (Bind Abst) x3)
                                                                               by (ex4_3_intro . . . . . . . . . . previous H14 H15 H16)
                                                                               we proved 
                                                                                  ex4_3
                                                                                    C
                                                                                    T
                                                                                    A
                                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                               by (or3_intro1 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro2 : H12:ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex2_2_intro : x2:C x3:T H13:drop n O x0 (CHead x2 (Bind Void) x3) H14:csuba g x2 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x2 (Bind Void) x3)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x2 (Bind Void) x3)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x2 (Bind Void) x3)
                                                                               by (ex2_2_intro . . . . . . previous H14)
                                                                               we proved 
                                                                                  ex2_2
                                                                                    C
                                                                                    T
                                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                               by (or3_intro2 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                             we proved 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                             by (eq_ind_r . . . previous . H9)

                                                                or3
                                                                  ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                           we proved 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                           csuba g c2 (CHead c (Bind Abbr) t)
                                             (drop (r (Bind Abbr) n) O c (CHead d1 (Bind Abbr) u1)
                                                  (or3
                                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                       ex4_3
                                                         C
                                                         T
                                                         A
                                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1))
                                         suppose H5csuba g c2 (CHead c (Bind Abst) t)
                                         suppose H6drop (r (Bind Abst) n) O c (CHead d1 (Bind Abbr) u1)
                                           (H_x
                                              by (csuba_gen_abst_rev . . . . H5)

                                                 or
                                                   ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abst) t) λd2:C.csuba g d2 c
                                                   ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 c
                                           end of H_x
                                           (H7consider H_x
                                           we proceed by induction on H7 to prove 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case or_introl : H8:ex2 C λd2:C.eq C c2 (CHead d2 (Bind Abst) t) λd2:C.csuba g d2 c 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    we proceed by induction on H8 to prove 
                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                       case ex_intro2 : x:C H9:eq C c2 (CHead x (Bind Abst) t) H10:csuba g x c 
                                                          the thesis becomes 
                                                          or3
                                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             (H11
                                                                consider H6
                                                                we proved drop (r (Bind Abst) n) O c (CHead d1 (Bind Abbr) u1)
                                                                that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                                by (H . . . previous . . H10)

                                                                   or3
                                                                     ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             end of H11
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro0 : H12:ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex_intro2 : x0:C H13:drop n O x (CHead x0 (Bind Abbr) u1) H14:csuba g x0 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Abbr) u1)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x (CHead x0 (Bind Abbr) u1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abst) t) (CHead x0 (Bind Abbr) u1)
                                                                               by (ex_intro2 . . . . previous H14)
                                                                               we proved 
                                                                                  ex2
                                                                                    C
                                                                                    λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                    λd2:C.csuba g d2 d1
                                                                               by (or3_intro0 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro1 : H12:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex4_3_intro : x0:C x1:T x2:A H13:drop n O x (CHead x0 (Bind Abst) x1) H14:csuba g x0 d1 H15:arity g x0 x1 (asucc g x2) H16:arity g d1 u1 x2 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Abst) x1)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x (CHead x0 (Bind Abst) x1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abst) t) (CHead x0 (Bind Abst) x1)
                                                                               by (ex4_3_intro . . . . . . . . . . previous H14 H15 H16)
                                                                               we proved 
                                                                                  ex4_3
                                                                                    C
                                                                                    T
                                                                                    A
                                                                                    λd2:C
                                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                               by (or3_intro1 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro2 : H12:ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex2_2_intro : x0:C x1:T H13:drop n O x (CHead x0 (Bind Void) x1) H14:csuba g x0 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C
                                                                                  .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x (CHead x0 (Bind Void) x1)
                                                                               that is equivalent to drop (r (Bind Abst) n) O x (CHead x0 (Bind Void) x1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x (Bind Abst) t) (CHead x0 (Bind Void) x1)
                                                                               by (ex2_2_intro . . . . . . previous H14)
                                                                               we proved 
                                                                                  ex2_2
                                                                                    C
                                                                                    T
                                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                               by (or3_intro2 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C
                                                                                        .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                             we proved 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Abst) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                             by (eq_ind_r . . . previous . H9)

                                                                or3
                                                                  ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case or_intror : H8:ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 c 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    we proceed by induction on H8 to prove 
                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                       case ex2_2_intro : x0:C x1:T H9:eq C c2 (CHead x0 (Bind Void) x1) H10:csuba g x0 c 
                                                          the thesis becomes 
                                                          or3
                                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             (H11
                                                                consider H6
                                                                we proved drop (r (Bind Abst) n) O c (CHead d1 (Bind Abbr) u1)
                                                                that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                                by (H . . . previous . . H10)

                                                                   or3
                                                                     ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                             end of H11
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro0 : H12:ex2 C λd2:C.drop n O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex_intro2 : x:C H13:drop n O x0 (CHead x (Bind Abbr) u1) H14:csuba g x d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x (Bind Abbr) u1)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x (Bind Abbr) u1)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x (Bind Abbr) u1)
                                                                               by (ex_intro2 . . . . previous H14)
                                                                               we proved 
                                                                                  ex2
                                                                                    C
                                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                    λd2:C.csuba g d2 d1
                                                                               by (or3_intro0 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro1 : H12:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x0 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex4_3_intro : x2:C x3:T x4:A H13:drop n O x0 (CHead x2 (Bind Abst) x3) H14:csuba g x2 d1 H15:arity g x2 x3 (asucc g x4) H16:arity g d1 u1 x4 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x2 (Bind Abst) x3)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x2 (Bind Abst) x3)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x2 (Bind Abst) x3)
                                                                               by (ex4_3_intro . . . . . . . . . . previous H14 H15 H16)
                                                                               we proved 
                                                                                  ex4_3
                                                                                    C
                                                                                    T
                                                                                    A
                                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                               by (or3_intro1 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                case or3_intro2 : H12:ex2_2 C T λd2:C.λu2:T.drop n O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      we proceed by induction on H12 to prove 
                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                                         case ex2_2_intro : x2:C x3:T H13:drop n O x0 (CHead x2 (Bind Void) x3) H14:csuba g x2 d1 
                                                                            the thesis becomes 
                                                                            or3
                                                                              ex2
                                                                                C
                                                                                λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                λd2:C.csuba g d2 d1
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                              ex2_2
                                                                                C
                                                                                T
                                                                                λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                λd2:C.λ:T.csuba g d2 d1
                                                                               consider H13
                                                                               we proved drop n O x0 (CHead x2 (Bind Void) x3)
                                                                               that is equivalent to drop (r (Bind Void) n) O x0 (CHead x2 (Bind Void) x3)
                                                                               by (drop_drop . . . . previous .)
                                                                               we proved drop (S n) O (CHead x0 (Bind Void) x1) (CHead x2 (Bind Void) x3)
                                                                               by (ex2_2_intro . . . . . . previous H14)
                                                                               we proved 
                                                                                  ex2_2
                                                                                    C
                                                                                    T
                                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                               by (or3_intro2 . . . previous)

                                                                                  or3
                                                                                    ex2
                                                                                      C
                                                                                      λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                                      λd2:C.csuba g d2 d1
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                                    ex2_2
                                                                                      C
                                                                                      T
                                                                                      λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                                      λd2:C.λ:T.csuba g d2 d1

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1
                                                             we proved 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Bind Void) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                             by (eq_ind_r . . . previous . H9)

                                                                or3
                                                                  ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                           we proved 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                           csuba g c2 (CHead c (Bind Abst) t)
                                             (drop (r (Bind Abst) n) O c (CHead d1 (Bind Abbr) u1)
                                                  (or3
                                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                       ex4_3
                                                         C
                                                         T
                                                         A
                                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1))
                                         suppose H5csuba g c2 (CHead c (Bind Void) t)
                                         suppose H6drop (r (Bind Void) n) O c (CHead d1 (Bind Abbr) u1)
                                           (H_x
                                              by (csuba_gen_void_rev . . . . H5)
ex2 C λd2:C.eq C c2 (CHead d2 (Bind Void) t) λd2:C.csuba g d2 c
                                           end of H_x
                                           (H7consider H_x
                                           we proceed by induction on H7 to prove 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                              case ex_intro2 : x:C H8:eq C c2 (CHead x (Bind Void) t) H9:csuba g x c 
                                                 the thesis becomes 
                                                 or3
                                                   ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                                   ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    (H10
                                                       consider H6
                                                       we proved drop (r (Bind Void) n) O c (CHead d1 (Bind Abbr) u1)
                                                       that is equivalent to drop n O c (CHead d1 (Bind Abbr) u1)
                                                       by (H . . . previous . . H9)

                                                          or3
                                                            ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                    end of H10
                                                    we proceed by induction on H10 to prove 
                                                       or3
                                                         ex2
                                                           C
                                                           λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                           λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C
                                                             .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2
                                                           C
                                                           T
                                                           λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                           λd2:C.λ:T.csuba g d2 d1
                                                       case or3_intro0 : H11:ex2 C λd2:C.drop n O x (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                          the thesis becomes 
                                                          or3
                                                            ex2
                                                              C
                                                              λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                              λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C
                                                                .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2
                                                              C
                                                              T
                                                              λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                              λd2:C.λ:T.csuba g d2 d1
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case ex_intro2 : x0:C H12:drop n O x (CHead x0 (Bind Abbr) u1) H13:csuba g x0 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      consider H12
                                                                      we proved drop n O x (CHead x0 (Bind Abbr) u1)
                                                                      that is equivalent to drop (r (Bind Void) n) O x (CHead x0 (Bind Abbr) u1)
                                                                      by (drop_drop . . . . previous .)
                                                                      we proved drop (S n) O (CHead x (Bind Void) t) (CHead x0 (Bind Abbr) u1)
                                                                      by (ex_intro2 . . . . previous H13)
                                                                      we proved 
                                                                         ex2
                                                                           C
                                                                           λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                           λd2:C.csuba g d2 d1
                                                                      by (or3_intro0 . . . previous)

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1

                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                       case or3_intro1 : H11:ex4_3 C T A λd2:C.λu2:T.λ:A.drop n O x (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                          the thesis becomes 
                                                          or3
                                                            ex2
                                                              C
                                                              λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                              λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C
                                                                .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2
                                                              C
                                                              T
                                                              λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                              λd2:C.λ:T.csuba g d2 d1
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case ex4_3_intro : x0:C x1:T x2:A H12:drop n O x (CHead x0 (Bind Abst) x1) H13:csuba g x0 d1 H14:arity g x0 x1 (asucc g x2) H15:arity g d1 u1 x2 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      consider H12
                                                                      we proved drop n O x (CHead x0 (Bind Abst) x1)
                                                                      that is equivalent to drop (r (Bind Void) n) O x (CHead x0 (Bind Abst) x1)
                                                                      by (drop_drop . . . . previous .)
                                                                      we proved drop (S n) O (CHead x (Bind Void) t) (CHead x0 (Bind Abst) x1)
                                                                      by (ex4_3_intro . . . . . . . . . . previous H13 H14 H15)
                                                                      we proved 
                                                                         ex4_3
                                                                           C
                                                                           T
                                                                           A
                                                                           λd2:C
                                                                             .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                      by (or3_intro1 . . . previous)

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1

                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                       case or3_intro2 : H11:ex2_2 C T λd2:C.λu2:T.drop n O x (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                          the thesis becomes 
                                                          or3
                                                            ex2
                                                              C
                                                              λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                              λd2:C.csuba g d2 d1
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C
                                                                .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                                            ex2_2
                                                              C
                                                              T
                                                              λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                              λd2:C.λ:T.csuba g d2 d1
                                                             we proceed by induction on H11 to prove 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                case ex2_2_intro : x0:C x1:T H12:drop n O x (CHead x0 (Bind Void) x1) H13:csuba g x0 d1 
                                                                   the thesis becomes 
                                                                   or3
                                                                     ex2
                                                                       C
                                                                       λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                       λd2:C.csuba g d2 d1
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C
                                                                         .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                     ex2_2
                                                                       C
                                                                       T
                                                                       λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                       λd2:C.λ:T.csuba g d2 d1
                                                                      consider H12
                                                                      we proved drop n O x (CHead x0 (Bind Void) x1)
                                                                      that is equivalent to drop (r (Bind Void) n) O x (CHead x0 (Bind Void) x1)
                                                                      by (drop_drop . . . . previous .)
                                                                      we proved drop (S n) O (CHead x (Bind Void) t) (CHead x0 (Bind Void) x1)
                                                                      by (ex2_2_intro . . . . . . previous H13)
                                                                      we proved 
                                                                         ex2_2
                                                                           C
                                                                           T
                                                                           λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                           λd2:C.λ:T.csuba g d2 d1
                                                                      by (or3_intro2 . . . previous)

                                                                         or3
                                                                           ex2
                                                                             C
                                                                             λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                             λd2:C.csuba g d2 d1
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C
                                                                               .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                           ex2_2
                                                                             C
                                                                             T
                                                                             λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                             λd2:C.λ:T.csuba g d2 d1

                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C
                                                                      .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                    we proved 
                                                       or3
                                                         ex2
                                                           C
                                                           λd2:C.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abbr) u1)
                                                           λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C
                                                             .λu2:T.λ:A.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2
                                                           C
                                                           T
                                                           λd2:C.λu2:T.drop (S n) O (CHead x (Bind Void) t) (CHead d2 (Bind Void) u2)
                                                           λd2:C.λ:T.csuba g d2 d1
                                                    by (eq_ind_r . . . previous . H8)

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                           we proved 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                           csuba g c2 (CHead c (Bind Void) t)
                                             (drop (r (Bind Void) n) O c (CHead d1 (Bind Abbr) u1)
                                                  (or3
                                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                       ex4_3
                                                         C
                                                         T
                                                         A
                                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1))
                                        by (previous . H3 H4)
                                        we proved 
                                           or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                        H3:csuba g c2 (CHead c (Bind b) t)
                                          .H4:drop (r (Bind b) n) O c (CHead d1 (Bind Abbr) u1)
                                            .or3
                                              ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                              ex4_3
                                                C
                                                T
                                                A
                                                λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                              ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                     assume fF
                                      suppose H3csuba g c2 (CHead c (Flat f) t)
                                      suppose H4drop (r (Flat f) n) O c (CHead d1 (Bind Abbr) u1)
                                        (H_x
                                           by (csuba_gen_flat_rev . . . . . H3)
ex2_2 C T λd2:C.λu2:T.eq C c2 (CHead d2 (Flat f) u2) λd2:C.λ:T.csuba g d2 c
                                        end of H_x
                                        (H5consider H_x
                                        we proceed by induction on H5 to prove 
                                           or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                           case ex2_2_intro : x0:C x1:T H6:eq C c2 (CHead x0 (Flat f) x1) H7:csuba g x0 c 
                                              the thesis becomes 
                                              or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                 (H8
                                                    consider H4
                                                    we proved drop (r (Flat f) n) O c (CHead d1 (Bind Abbr) u1)
                                                    that is equivalent to drop (S n) O c (CHead d1 (Bind Abbr) u1)
                                                    by (H0 . . previous . . H7)

                                                       or3
                                                         ex2 C λd2:C.drop (S n) O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O x0 (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2 C T λd2:C.λu2:T.drop (S n) O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                                 end of H8
                                                 we proceed by induction on H8 to prove 
                                                    or3
                                                      ex2
                                                        C
                                                        λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                        λd2:C.csuba g d2 d1
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                                      ex2_2
                                                        C
                                                        T
                                                        λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                        λd2:C.λ:T.csuba g d2 d1
                                                    case or3_intro0 : H9:ex2 C λd2:C.drop (S n) O x0 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1 
                                                       the thesis becomes 
                                                       or3
                                                         ex2
                                                           C
                                                           λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                           λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2
                                                           C
                                                           T
                                                           λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                           λd2:C.λ:T.csuba g d2 d1
                                                          we proceed by induction on H9 to prove 
                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                             case ex_intro2 : x:C H10:drop (S n) O x0 (CHead x (Bind Abbr) u1) H11:csuba g x d1 
                                                                the thesis becomes 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                   consider H10
                                                                   we proved drop (S n) O x0 (CHead x (Bind Abbr) u1)
                                                                   that is equivalent to drop (r (Flat f) n) O x0 (CHead x (Bind Abbr) u1)
                                                                   by (drop_drop . . . . previous .)
                                                                   we proved drop (S n) O (CHead x0 (Flat f) x1) (CHead x (Bind Abbr) u1)
                                                                   by (ex_intro2 . . . . previous H11)
                                                                   we proved 
                                                                      ex2
                                                                        C
                                                                        λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                        λd2:C.csuba g d2 d1
                                                                   by (or3_intro0 . . . previous)

                                                                      or3
                                                                        ex2
                                                                          C
                                                                          λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                          λd2:C.csuba g d2 d1
                                                                        ex4_3
                                                                          C
                                                                          T
                                                                          A
                                                                          λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                          λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                          λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                          λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                        ex2_2
                                                                          C
                                                                          T
                                                                          λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                          λd2:C.λ:T.csuba g d2 d1

                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                    case or3_intro1 : H9:ex4_3 C T A λd2:C.λu2:T.λ:A.drop (S n) O x0 (CHead d2 (Bind Abst) u2) λd2:C.λ:T.λ:A.csuba g d2 d1 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a) λ:C.λ:T.λa:A.arity g d1 u1 a 
                                                       the thesis becomes 
                                                       or3
                                                         ex2
                                                           C
                                                           λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                           λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2
                                                           C
                                                           T
                                                           λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                           λd2:C.λ:T.csuba g d2 d1
                                                          we proceed by induction on H9 to prove 
                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                             case ex4_3_intro : x2:C x3:T x4:A H10:drop (S n) O x0 (CHead x2 (Bind Abst) x3) H11:csuba g x2 d1 H12:arity g x2 x3 (asucc g x4) H13:arity g d1 u1 x4 
                                                                the thesis becomes 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                   consider H10
                                                                   we proved drop (S n) O x0 (CHead x2 (Bind Abst) x3)
                                                                   that is equivalent to drop (r (Flat f) n) O x0 (CHead x2 (Bind Abst) x3)
                                                                   by (drop_drop . . . . previous .)
                                                                   we proved drop (S n) O (CHead x0 (Flat f) x1) (CHead x2 (Bind Abst) x3)
                                                                   by (ex4_3_intro . . . . . . . . . . previous H11 H12 H13)
                                                                   we proved 
                                                                      ex4_3
                                                                        C
                                                                        T
                                                                        A
                                                                        λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                   by (or3_intro1 . . . previous)

                                                                      or3
                                                                        ex2
                                                                          C
                                                                          λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                          λd2:C.csuba g d2 d1
                                                                        ex4_3
                                                                          C
                                                                          T
                                                                          A
                                                                          λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                          λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                          λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                          λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                        ex2_2
                                                                          C
                                                                          T
                                                                          λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                          λd2:C.λ:T.csuba g d2 d1

                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                    case or3_intro2 : H9:ex2_2 C T λd2:C.λu2:T.drop (S n) O x0 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1 
                                                       the thesis becomes 
                                                       or3
                                                         ex2
                                                           C
                                                           λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                           λd2:C.csuba g d2 d1
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d2 d1
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                           λ:C.λ:T.λa:A.arity g d1 u1 a
                                                         ex2_2
                                                           C
                                                           T
                                                           λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                           λd2:C.λ:T.csuba g d2 d1
                                                          we proceed by induction on H9 to prove 
                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                             case ex2_2_intro : x2:C x3:T H10:drop (S n) O x0 (CHead x2 (Bind Void) x3) H11:csuba g x2 d1 
                                                                the thesis becomes 
                                                                or3
                                                                  ex2
                                                                    C
                                                                    λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                    λd2:C.csuba g d2 d1
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                  ex2_2
                                                                    C
                                                                    T
                                                                    λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                    λd2:C.λ:T.csuba g d2 d1
                                                                   consider H10
                                                                   we proved drop (S n) O x0 (CHead x2 (Bind Void) x3)
                                                                   that is equivalent to drop (r (Flat f) n) O x0 (CHead x2 (Bind Void) x3)
                                                                   by (drop_drop . . . . previous .)
                                                                   we proved drop (S n) O (CHead x0 (Flat f) x1) (CHead x2 (Bind Void) x3)
                                                                   by (ex2_2_intro . . . . . . previous H11)
                                                                   we proved 
                                                                      ex2_2
                                                                        C
                                                                        T
                                                                        λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                        λd2:C.λ:T.csuba g d2 d1
                                                                   by (or3_intro2 . . . previous)

                                                                      or3
                                                                        ex2
                                                                          C
                                                                          λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                          λd2:C.csuba g d2 d1
                                                                        ex4_3
                                                                          C
                                                                          T
                                                                          A
                                                                          λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                          λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                          λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                          λ:C.λ:T.λa:A.arity g d1 u1 a
                                                                        ex2_2
                                                                          C
                                                                          T
                                                                          λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                          λd2:C.λ:T.csuba g d2 d1

                                                             or3
                                                               ex2
                                                                 C
                                                                 λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                                 λd2:C.csuba g d2 d1
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d2 d1
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 a
                                                               ex2_2
                                                                 C
                                                                 T
                                                                 λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                                 λd2:C.λ:T.csuba g d2 d1
                                                 we proved 
                                                    or3
                                                      ex2
                                                        C
                                                        λd2:C.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abbr) u1)
                                                        λd2:C.csuba g d2 d1
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Abst) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                                      ex2_2
                                                        C
                                                        T
                                                        λd2:C.λu2:T.drop (S n) O (CHead x0 (Flat f) x1) (CHead d2 (Bind Void) u2)
                                                        λd2:C.λ:T.csuba g d2 d1
                                                 by (eq_ind_r . . . previous . H6)

                                                    or3
                                                      ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d2 d1
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                        λ:C.λ:T.λa:A.arity g d1 u1 a
                                                      ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                        we proved 
                                           or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                        H3:csuba g c2 (CHead c (Flat f) t)
                                          .H4:drop (r (Flat f) n) O c (CHead d1 (Bind Abbr) u1)
                                            .or3
                                              ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                              ex4_3
                                                C
                                                T
                                                A
                                                λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                λd2:C.λ:T.λ:A.csuba g d2 d1
                                                λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                λ:C.λ:T.λa:A.arity g d1 u1 a
                                              ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                                  by (previous . H2 previous)
                                  we proved 
                                     or3
                                       ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                       ex4_3
                                         C
                                         T
                                         A
                                         λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                         λd2:C.λ:T.λ:A.csuba g d2 d1
                                         λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                         λ:C.λ:T.λa:A.arity g d1 u1 a
                                       ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1

                                  d1:C
                                    .u1:T
                                      .H1:drop (S n) O (CHead c k t) (CHead d1 (Bind Abbr) u1)
                                        .g:G
                                          .c2:C
                                            .H2:csuba g c2 (CHead c k t)
                                              .or3
                                                ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d2 d1
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                                  λ:C.λ:T.λa:A.arity g d1 u1 a
                                                ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1
                      we proved 
                         d1:C
                           .u1:T
                             .drop (S n) O c1 (CHead d1 (Bind Abbr) u1)
                               g:G
                                    .c2:C
                                      .csuba g c2 c1
                                        (or3
                                             ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                               λd2:C.λ:T.λ:A.csuba g d2 d1
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                               λ:C.λ:T.λa:A.arity g d1 u1 a
                                             ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)

                      c1:C
                        .d1:C
                          .u1:T
                            .drop (S n) O c1 (CHead d1 (Bind Abbr) u1)
                              g:G
                                   .c2:C
                                     .csuba g c2 c1
                                       (or3
                                            ex2 C λd2:C.drop (S n) O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                            ex4_3
                                              C
                                              T
                                              A
                                              λd2:C.λu2:T.λ:A.drop (S n) O c2 (CHead d2 (Bind Abst) u2)
                                              λd2:C.λ:T.λ:A.csuba g d2 d1
                                              λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                              λ:C.λ:T.λa:A.arity g d1 u1 a
                                            ex2_2 C T λd2:C.λu2:T.drop (S n) O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
          we proved 
             c1:C
               .d1:C
                 .u1:T
                   .drop i O c1 (CHead d1 (Bind Abbr) u1)
                     g:G
                          .c2:C
                            .csuba g c2 c1
                              (or3
                                   ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                   ex4_3
                                     C
                                     T
                                     A
                                     λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abst) u2)
                                     λd2:C.λ:T.λ:A.csuba g d2 d1
                                     λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                     λ:C.λ:T.λa:A.arity g d1 u1 a
                                   ex2_2 C T λd2:C.λu2:T.drop i O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)
       we proved 
          i:nat
            .c1:C
              .d1:C
                .u1:T
                  .drop i O c1 (CHead d1 (Bind Abbr) u1)
                    g:G
                         .c2:C
                           .csuba g c2 c1
                             (or3
                                  ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abbr) u1) λd2:C.csuba g d2 d1
                                  ex4_3
                                    C
                                    T
                                    A
                                    λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abst) u2)
                                    λd2:C.λ:T.λ:A.csuba g d2 d1
                                    λd2:C.λu2:T.λa:A.arity g d2 u2 (asucc g a)
                                    λ:C.λ:T.λa:A.arity g d1 u1 a
                                  ex2_2 C T λd2:C.λu2:T.drop i O c2 (CHead d2 (Bind Void) u2) λd2:C.λ:T.csuba g d2 d1)