DEFINITION csuba_getl_abst()
TYPE =
       ∀g:G
         .∀c1:C
           .∀d1:C
             .∀u1:T
               .∀i:nat
                 .getl i c1 (CHead d1 (Bind Abst) u1)
                   →∀c2:C
                        .csuba g c1 c2
                          →(or
                               ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                               ex4_3
                                 C
                                 T
                                 A
                                 λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                 λd2:C.λ:T.λ:A.csuba g d1 d2
                                 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                 λd2:C.λu2:T.λa:A.arity g d2 u2 a)
BODY =
        assume g: G
        assume c1: C
        assume d1: C
        assume u1: T
        assume i: nat
        suppose H: getl i c1 (CHead d1 (Bind Abst) u1)
          (H0) 
             by (getl_gen_all . . . H)
ex2 C λe:C.drop i O c1 e λe:C.clear e (CHead d1 (Bind Abst) u1)
          end of H0
          we proceed by induction on H0 to prove 
             ∀c2:C
               .csuba g c1 c2
                 →(or
                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                      ex4_3
                        C
                        T
                        A
                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                        λd2:C.λ:T.λ:A.csuba g d1 d2
                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                        λd2:C.λu2:T.λa:A.arity g d2 u2 a)
             case ex_intro2 : x:C H1:drop i O c1 x H2:clear x (CHead d1 (Bind Abst) u1) ⇒
                the thesis becomes 
                ∀c2:C
                  .csuba g c1 c2
                    →(or
                         ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                         ex4_3
                           C
                           T
                           A
                           λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                           λd2:C.λ:T.λ:A.csuba g d1 d2
                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                           λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                      assume n: nat
                       suppose : drop i O c1 (CSort n)
                       suppose H4: clear (CSort n) (CHead d1 (Bind Abst) u1)
                         by (clear_gen_sort . . H4 .)
                         we proved 
                            ∀c2:C
                              .csuba g c1 c2
                                →(or
                                     ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                     ex4_3
                                       C
                                       T
                                       A
                                       λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a)

                         drop i O c1 (CSort n)
                           →∀H4:clear (CSort n) (CHead d1 (Bind Abst) u1)
                                .∀c2:C
                                  .csuba g c1 c2
                                    →(or
                                         ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                         ex4_3
                                           C
                                           T
                                           A
                                           λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                    assume x0: C
                    suppose : 
                       drop i O c1 x0
                         →(clear x0 (CHead d1 (Bind Abst) u1)
                              →∀c2:C
                                   .csuba g c1 c2
                                     →(or
                                          ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                          ex4_3
                                            C
                                            T
                                            A
                                            λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                            λd2:C.λ:T.λ:A.csuba g d1 d2
                                            λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                            λd2:C.λu2:T.λa:A.arity g d2 u2 a))
                    assume k: K
                       assume t: T
                       suppose H3: drop i O c1 (CHead x0 k t)
                       suppose H4: clear (CHead x0 k t) (CHead d1 (Bind Abst) u1)
                            assume b: B
                             suppose H5: drop i O c1 (CHead x0 (Bind b) t)
                             suppose H6: clear (CHead x0 (Bind b) t) (CHead d1 (Bind Abst) u1)
                               (H7) 
                                  by (clear_gen_bind . . . . H6)
                                  we proved eq C (CHead d1 (Bind Abst) u1) (CHead x0 (Bind b) t)
                                  by (f_equal . . . . . previous)
                                  we proved 
                                     eq
                                       C
                                       <λ:C.C> CASE CHead d1 (Bind Abst) u1 OF CSort ⇒d1 | CHead c  ⇒c
                                       <λ:C.C> CASE CHead x0 (Bind b) t OF CSort ⇒d1 | CHead c  ⇒c

                                     eq
                                       C
                                       λe:C.<λ:C.C> CASE e OF CSort ⇒d1 | CHead c  ⇒c (CHead d1 (Bind Abst) u1)
                                       λe:C.<λ:C.C> CASE e OF CSort ⇒d1 | CHead c  ⇒c (CHead x0 (Bind b) t)
                               end of H7
                               (h1) 
                                  (H8) 
                                     by (clear_gen_bind . . . . H6)
                                     we proved eq C (CHead d1 (Bind Abst) u1) (CHead x0 (Bind b) t)
                                     by (f_equal . . . . . previous)
                                     we proved 
                                        eq
                                          B
                                          <λ:C.B>
                                            CASE CHead d1 (Bind Abst) u1 OF
                                              CSort ⇒Abst
                                            | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst
                                          <λ:C.B>
                                            CASE CHead x0 (Bind b) t OF
                                              CSort ⇒Abst
                                            | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst

                                        eq
                                          B
                                          λe:C
                                              .<λ:C.B>
                                                CASE e OF
                                                  CSort ⇒Abst
                                                | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst
                                            CHead d1 (Bind Abst) u1
                                          λe:C
                                              .<λ:C.B>
                                                CASE e OF
                                                  CSort ⇒Abst
                                                | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst
                                            CHead x0 (Bind b) t
                                  end of H8
                                  (h1) 
                                     (H9) 
                                        by (clear_gen_bind . . . . H6)
                                        we proved eq C (CHead d1 (Bind Abst) u1) (CHead x0 (Bind b) t)
                                        by (f_equal . . . . . previous)
                                        we proved 
                                           eq
                                             T
                                             <λ:C.T> CASE CHead d1 (Bind Abst) u1 OF CSort ⇒u1 | CHead   t0⇒t0
                                             <λ:C.T> CASE CHead x0 (Bind b) t OF CSort ⇒u1 | CHead   t0⇒t0

                                           eq
                                             T
                                             λe:C.<λ:C.T> CASE e OF CSort ⇒u1 | CHead   t0⇒t0 (CHead d1 (Bind Abst) u1)
                                             λe:C.<λ:C.T> CASE e OF CSort ⇒u1 | CHead   t0⇒t0 (CHead x0 (Bind b) t)
                                     end of H9
                                      suppose H10: eq B Abst b
                                      suppose H11: eq C d1 x0
                                      assume c2: C
                                      suppose H12: csuba g c1 c2
                                        (H13) 
                                           consider H9
                                           we proved 
                                              eq
                                                T
                                                <λ:C.T> CASE CHead d1 (Bind Abst) u1 OF CSort ⇒u1 | CHead   t0⇒t0
                                                <λ:C.T> CASE CHead x0 (Bind b) t OF CSort ⇒u1 | CHead   t0⇒t0
                                           that is equivalent to eq T u1 t
                                           by (eq_ind_r . . . H5 . previous)
drop i O c1 (CHead x0 (Bind b) u1)
                                        end of H13
                                        (H14) 
                                           by (eq_ind_r . . . H13 . H10)
drop i O c1 (CHead x0 (Bind Abst) u1)
                                        end of H14
                                        (H15) 
                                           by (eq_ind_r . . . H14 . H11)
drop i O c1 (CHead d1 (Bind Abst) u1)
                                        end of H15
                                        (H16) 
                                           by (csuba_drop_abst . . . . H15 . . H12)

                                              or
                                                ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abbr) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d1 d2
                                                  λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                        end of H16
                                        we proceed by induction on H16 to prove 
                                           or
                                             ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                               λd2:C.λ:T.λ:A.csuba g d1 d2
                                               λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                           case or_introl : H17:ex2 C λd2:C.drop i O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2 ⇒
                                              the thesis becomes 
                                              or
                                                ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d1 d2
                                                  λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                 we proceed by induction on H17 to prove 
                                                    or
                                                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d1 d2
                                                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                    case ex_intro2 : x1:C H18:drop i O c2 (CHead x1 (Bind Abst) u1) H19:csuba g d1 x1 ⇒
                                                       the thesis becomes 
                                                       or
                                                         ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                          by (clear_bind . . .)
                                                          we proved clear (CHead x1 (Bind Abst) u1) (CHead x1 (Bind Abst) u1)
                                                          by (getl_intro . . . . H18 previous)
                                                          we proved getl i c2 (CHead x1 (Bind Abst) u1)
                                                          by (ex_intro2 . . . . previous H19)
                                                          we proved ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                          by (or_introl . . previous)

                                                             or
                                                               ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 a

                                                    or
                                                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d1 d2
                                                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                           case or_intror : H17:ex4_3 C T A λd2:C.λu2:T.λ:A.drop i O c2 (CHead d2 (Bind Abbr) u2) λd2:C.λ:T.λ:A.csuba g d1 d2 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a) λd2:C.λu2:T.λa:A.arity g d2 u2 a ⇒
                                              the thesis becomes 
                                              or
                                                ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d1 d2
                                                  λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                 we proceed by induction on H17 to prove 
                                                    or
                                                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d1 d2
                                                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                    case ex4_3_intro : x1:C x2:T x3:A H18:drop i O c2 (CHead x1 (Bind Abbr) x2) H19:csuba g d1 x1 H20:arity g d1 u1 (asucc g x3) H21:arity g x1 x2 x3 ⇒
                                                       the thesis becomes 
                                                       or
                                                         ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                          by (clear_bind . . .)
                                                          we proved clear (CHead x1 (Bind Abbr) x2) (CHead x1 (Bind Abbr) x2)
                                                          by (getl_intro . . . . H18 previous)
                                                          we proved getl i c2 (CHead x1 (Bind Abbr) x2)
                                                          by (ex4_3_intro . . . . . . . . . . previous H19 H20 H21)
                                                          we proved 
                                                             ex4_3
                                                               C
                                                               T
                                                               A
                                                               λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                               λd2:C.λ:T.λ:A.csuba g d1 d2
                                                               λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                               λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                          by (or_intror . . previous)

                                                             or
                                                               ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                               ex4_3
                                                                 C
                                                                 T
                                                                 A
                                                                 λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                                 λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 a

                                                    or
                                                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                      ex4_3
                                                        C
                                                        T
                                                        A
                                                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                        λd2:C.λ:T.λ:A.csuba g d1 d2
                                                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                        λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                        we proved 
                                           or
                                             ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                             ex4_3
                                               C
                                               T
                                               A
                                               λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                               λd2:C.λ:T.λ:A.csuba g d1 d2
                                               λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                               λd2:C.λu2:T.λa:A.arity g d2 u2 a

                                        eq B Abst b
                                          →(eq C d1 x0
                                               →∀c2:C
                                                    .csuba g c1 c2
                                                      →(or
                                                           ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                           ex4_3
                                                             C
                                                             T
                                                             A
                                                             λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a))
                                  end of h1
                                  (h2) 
                                     consider H8
                                     we proved 
                                        eq
                                          B
                                          <λ:C.B>
                                            CASE CHead d1 (Bind Abst) u1 OF
                                              CSort ⇒Abst
                                            | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst
                                          <λ:C.B>
                                            CASE CHead x0 (Bind b) t OF
                                              CSort ⇒Abst
                                            | CHead  k0 ⇒<λ:K.B> CASE k0 OF Bind b0⇒b0 | Flat ⇒Abst
eq B Abst b
                                  end of h2
                                  by (h1 h2)

                                     eq C d1 x0
                                       →∀c2:C
                                            .csuba g c1 c2
                                              →(or
                                                   ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d1 d2
                                                     λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                               end of h1
                               (h2) 
                                  consider H7
                                  we proved 
                                     eq
                                       C
                                       <λ:C.C> CASE CHead d1 (Bind Abst) u1 OF CSort ⇒d1 | CHead c  ⇒c
                                       <λ:C.C> CASE CHead x0 (Bind b) t OF CSort ⇒d1 | CHead c  ⇒c
eq C d1 x0
                               end of h2
                               by (h1 h2)
                               we proved 
                                  ∀c2:C
                                    .csuba g c1 c2
                                      →(or
                                           ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                           ex4_3
                                             C
                                             T
                                             A
                                             λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a)

                               ∀H5:drop i O c1 (CHead x0 (Bind b) t)
                                 .∀H6:clear (CHead x0 (Bind b) t) (CHead d1 (Bind Abst) u1)
                                   .∀c2:C
                                     .csuba g c1 c2
                                       →(or
                                            ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                            ex4_3
                                              C
                                              T
                                              A
                                              λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                            assume f: F
                             suppose H5: drop i O c1 (CHead x0 (Flat f) t)
                             suppose H6: clear (CHead x0 (Flat f) t) (CHead d1 (Bind Abst) u1)
                               (H7) consider H5
                               we proceed by induction on i to prove 
                                  ∀x1:C
                                    .drop i O x1 (CHead x0 (Flat f) t)
                                      →∀c2:C
                                           .csuba g x1 c2
                                             →(or
                                                  ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                  ex4_3
                                                    C
                                                    T
                                                    A
                                                    λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                                  case O : ⇒
                                     the thesis becomes 
                                     ∀x1:C
                                       .drop O O x1 (CHead x0 (Flat f) t)
                                         →∀c2:C
                                              .csuba g x1 c2
                                                →(or
                                                     ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                     ex4_3
                                                       C
                                                       T
                                                       A
                                                       λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                                         assume x1: C
                                         suppose H8: drop O O x1 (CHead x0 (Flat f) t)
                                         assume c2: C
                                         suppose H9: csuba g x1 c2
                                           (H10) 
                                              by (drop_gen_refl . . H8)
                                              we proved eq C x1 (CHead x0 (Flat f) t)
                                              we proceed by induction on the previous result to prove csuba g (CHead x0 (Flat f) t) c2
                                                 case refl_equal : ⇒
                                                    the thesis becomes the hypothesis H9
csuba g (CHead x0 (Flat f) t) c2
                                           end of H10
                                           (H_y) 
                                              by (clear_gen_flat . . . . H6)
                                              we proved clear x0 (CHead d1 (Bind Abst) u1)
                                              by (clear_flat . . previous . .)
clear (CHead x0 (Flat f) t) (CHead d1 (Bind Abst) u1)
                                           end of H_y
                                           (H11) 
                                              by (csuba_clear_conf . . . H10 . H_y)
ex2 C λe2:C.csuba g (CHead d1 (Bind Abst) u1) e2 λe2:C.clear c2 e2
                                           end of H11
                                           we proceed by induction on H11 to prove 
                                              or
                                                ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d1 d2
                                                  λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                              case ex_intro2 : x2:C H12:csuba g (CHead d1 (Bind Abst) u1) x2 H13:clear c2 x2 ⇒
                                                 the thesis becomes 
                                                 or
                                                   ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d1 d2
                                                     λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                    (H_x) 
                                                       by (csuba_gen_abst . . . . H12)

                                                          or
                                                            ex2 C λd2:C.eq C x2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.eq C x2 (CHead d2 (Bind Abbr) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                    end of H_x
                                                    (H14) consider H_x
                                                    we proceed by induction on H14 to prove 
                                                       or
                                                         ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                       case or_introl : H15:ex2 C λd2:C.eq C x2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2 ⇒
                                                          the thesis becomes 
                                                          or
                                                            ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                             we proceed by induction on H15 to prove 
                                                                or
                                                                  ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                case ex_intro2 : x3:C H16:eq C x2 (CHead x3 (Bind Abst) u1) H17:csuba g d1 x3 ⇒
                                                                   the thesis becomes 
                                                                   or
                                                                     ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                      (H18) 
                                                                         we proceed by induction on H16 to prove clear c2 (CHead x3 (Bind Abst) u1)
                                                                            case refl_equal : ⇒
                                                                               the thesis becomes the hypothesis H13
clear c2 (CHead x3 (Bind Abst) u1)
                                                                      end of H18
                                                                      by (drop_refl .)
                                                                      we proved drop O O c2 c2
                                                                      by (getl_intro . . . . previous H18)
                                                                      we proved getl O c2 (CHead x3 (Bind Abst) u1)
                                                                      by (ex_intro2 . . . . previous H17)
                                                                      we proved ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                      by (or_introl . . previous)

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

                                                                or
                                                                  ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                       case or_intror : H15:ex4_3 C T A λd2:C.λu2:T.λ:A.eq C x2 (CHead d2 (Bind Abbr) u2) λd2:C.λ:T.λ:A.csuba g d1 d2 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a) λd2:C.λu2:T.λa:A.arity g d2 u2 a ⇒
                                                          the thesis becomes 
                                                          or
                                                            ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                             we proceed by induction on H15 to prove 
                                                                or
                                                                  ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                case ex4_3_intro : x3:C x4:T x5:A H16:eq C x2 (CHead x3 (Bind Abbr) x4) H17:csuba g d1 x3 H18:arity g d1 u1 (asucc g x5) H19:arity g x3 x4 x5 ⇒
                                                                   the thesis becomes 
                                                                   or
                                                                     ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                      (H20) 
                                                                         we proceed by induction on H16 to prove clear c2 (CHead x3 (Bind Abbr) x4)
                                                                            case refl_equal : ⇒
                                                                               the thesis becomes the hypothesis H13
clear c2 (CHead x3 (Bind Abbr) x4)
                                                                      end of H20
                                                                      by (drop_refl .)
                                                                      we proved drop O O c2 c2
                                                                      by (getl_intro . . . . previous H20)
                                                                      we proved getl O c2 (CHead x3 (Bind Abbr) x4)
                                                                      by (ex4_3_intro . . . . . . . . . . previous H17 H18 H19)
                                                                      we proved 
                                                                         ex4_3
                                                                           C
                                                                           T
                                                                           A
                                                                           λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                      by (or_intror . . previous)

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

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

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

                                           ∀x1:C
                                             .drop O O x1 (CHead x0 (Flat f) t)
                                               →∀c2:C
                                                    .csuba g x1 c2
                                                      →(or
                                                           ex2 C λd2:C.getl O c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                           ex4_3
                                                             C
                                                             T
                                                             A
                                                             λd2:C.λu2:T.λ:A.getl O c2 (CHead d2 (Bind Abbr) u2)
                                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                                  case S : n:nat ⇒
                                     the thesis becomes 
                                     ∀x1:C
                                       .∀H9:drop (S n) O x1 (CHead x0 (Flat f) t)
                                         .∀c2:C
                                           .∀H10:csuba g x1 c2
                                             .or
                                               ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                               ex4_3
                                                 C
                                                 T
                                                 A
                                                 λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                 λd2:C.λ:T.λ:A.csuba g d1 d2
                                                 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                 λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                     (H8) by induction hypothesis we know 
                                        ∀x1:C
                                          .drop n O x1 (CHead x0 (Flat f) t)
                                            →∀c2:C
                                                 .csuba g x1 c2
                                                   →(or
                                                        ex2 C λd2:C.getl n c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                        ex4_3
                                                          C
                                                          T
                                                          A
                                                          λd2:C.λu2:T.λ:A.getl n c2 (CHead d2 (Bind Abbr) u2)
                                                          λd2:C.λ:T.λ:A.csuba g d1 d2
                                                          λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                          λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                                         assume x1: C
                                         suppose H9: drop (S n) O x1 (CHead x0 (Flat f) t)
                                         assume c2: C
                                         suppose H10: csuba g x1 c2
                                           (H11) 
                                              by (drop_clear . . . H9)

                                                 ex2_3
                                                   B
                                                   C
                                                   T
                                                   λb:B.λe:C.λv:T.clear x1 (CHead e (Bind b) v)
                                                   λ:B.λe:C.λ:T.drop n O e (CHead x0 (Flat f) t)
                                           end of H11
                                           we proceed by induction on H11 to prove 
                                              or
                                                ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                ex4_3
                                                  C
                                                  T
                                                  A
                                                  λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                  λd2:C.λ:T.λ:A.csuba g d1 d2
                                                  λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                  λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                              case ex2_3_intro : x2:B x3:C x4:T H12:clear x1 (CHead x3 (Bind x2) x4) H13:drop n O x3 (CHead x0 (Flat f) t) ⇒
                                                 the thesis becomes 
                                                 or
                                                   ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                   ex4_3
                                                     C
                                                     T
                                                     A
                                                     λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                     λd2:C.λ:T.λ:A.csuba g d1 d2
                                                     λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                     λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                    (H14) 
                                                       by (csuba_clear_conf . . . H10 . H12)
ex2 C λe2:C.csuba g (CHead x3 (Bind x2) x4) e2 λe2:C.clear c2 e2
                                                    end of H14
                                                    we proceed by induction on H14 to prove 
                                                       or
                                                         ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                         ex4_3
                                                           C
                                                           T
                                                           A
                                                           λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                           λd2:C.λ:T.λ:A.csuba g d1 d2
                                                           λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                           λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                       case ex_intro2 : x5:C H15:csuba g (CHead x3 (Bind x2) x4) x5 H16:clear c2 x5 ⇒
                                                          the thesis becomes 
                                                          or
                                                            ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                            ex4_3
                                                              C
                                                              T
                                                              A
                                                              λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                             (H_x) 
                                                                by (csuba_gen_bind . . . . . H15)
ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C x5 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g x3 e2
                                                             end of H_x
                                                             (H17) consider H_x
                                                             we proceed by induction on H17 to prove 
                                                                or
                                                                  ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                  ex4_3
                                                                    C
                                                                    T
                                                                    A
                                                                    λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                case ex2_3_intro : x6:B x7:C x8:T H18:eq C x5 (CHead x7 (Bind x6) x8) H19:csuba g x3 x7 ⇒
                                                                   the thesis becomes 
                                                                   or
                                                                     ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                     ex4_3
                                                                       C
                                                                       T
                                                                       A
                                                                       λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                      (H20) 
                                                                         we proceed by induction on H18 to prove clear c2 (CHead x7 (Bind x6) x8)
                                                                            case refl_equal : ⇒
                                                                               the thesis becomes the hypothesis H16
clear c2 (CHead x7 (Bind x6) x8)
                                                                      end of H20
                                                                      (H21) 
                                                                         by (H8 . H13 . H19)

                                                                            or
                                                                              ex2 C λd2:C.getl n x7 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.getl n x7 (CHead d2 (Bind Abbr) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                      end of H21
                                                                      we proceed by induction on H21 to prove 
                                                                         or
                                                                           ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                           ex4_3
                                                                             C
                                                                             T
                                                                             A
                                                                             λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                         case or_introl : H22:ex2 C λd2:C.getl n x7 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2 ⇒
                                                                            the thesis becomes 
                                                                            or
                                                                              ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                               we proceed by induction on H22 to prove 
                                                                                  or
                                                                                    ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                                  case ex_intro2 : x9:C H23:getl n x7 (CHead x9 (Bind Abst) u1) H24:csuba g d1 x9 ⇒
                                                                                     the thesis becomes 
                                                                                     or
                                                                                       ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                       ex4_3
                                                                                         C
                                                                                         T
                                                                                         A
                                                                                         λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                         λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                         λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                         λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                                        by (getl_clear_bind . . . . H20 . . H23)
                                                                                        we proved getl (S n) c2 (CHead x9 (Bind Abst) u1)
                                                                                        by (ex_intro2 . . . . previous H24)
                                                                                        we proved ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                        by (or_introl . . previous)

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

                                                                                  or
                                                                                    ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                         case or_intror : H22:ex4_3 C T A λd2:C.λu2:T.λ:A.getl n x7 (CHead d2 (Bind Abbr) u2) λd2:C.λ:T.λ:A.csuba g d1 d2 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a) λd2:C.λu2:T.λa:A.arity g d2 u2 a ⇒
                                                                            the thesis becomes 
                                                                            or
                                                                              ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                              ex4_3
                                                                                C
                                                                                T
                                                                                A
                                                                                λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                               we proceed by induction on H22 to prove 
                                                                                  or
                                                                                    ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                    ex4_3
                                                                                      C
                                                                                      T
                                                                                      A
                                                                                      λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                      λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                      λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                      λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                                  case ex4_3_intro : x9:C x10:T x11:A H23:getl n x7 (CHead x9 (Bind Abbr) x10) H24:csuba g d1 x9 H25:arity g d1 u1 (asucc g x11) H26:arity g x9 x10 x11 ⇒
                                                                                     the thesis becomes 
                                                                                     or
                                                                                       ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                                                       ex4_3
                                                                                         C
                                                                                         T
                                                                                         A
                                                                                         λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                         λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                         λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                         λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                                        by (getl_clear_bind . . . . H20 . . H23)
                                                                                        we proved getl (S n) c2 (CHead x9 (Bind Abbr) x10)
                                                                                        by (ex4_3_intro . . . . . . . . . . previous H24 H25 H26)
                                                                                        we proved 
                                                                                           ex4_3
                                                                                             C
                                                                                             T
                                                                                             A
                                                                                             λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                                                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a
                                                                                        by (or_intror . . previous)

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

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

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

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

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

                                           ∀x1:C
                                             .∀H9:drop (S n) O x1 (CHead x0 (Flat f) t)
                                               .∀c2:C
                                                 .∀H10:csuba g x1 c2
                                                   .or
                                                     ex2 C λd2:C.getl (S n) c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                     ex4_3
                                                       C
                                                       T
                                                       A
                                                       λd2:C.λu2:T.λ:A.getl (S n) c2 (CHead d2 (Bind Abbr) u2)
                                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a
                               we proved 
                                  ∀x1:C
                                    .drop i O x1 (CHead x0 (Flat f) t)
                                      →∀c2:C
                                           .csuba g x1 c2
                                             →(or
                                                  ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                                  ex4_3
                                                    C
                                                    T
                                                    A
                                                    λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                               by (unintro . . . previous H7)
                               we proved 
                                  ∀c2:C
                                    .csuba g c1 c2
                                      →(or
                                           ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                           ex4_3
                                             C
                                             T
                                             A
                                             λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                             λd2:C.λ:T.λ:A.csuba g d1 d2
                                             λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                             λd2:C.λu2:T.λa:A.arity g d2 u2 a)

                               ∀H5:drop i O c1 (CHead x0 (Flat f) t)
                                 .∀H6:clear (CHead x0 (Flat f) t) (CHead d1 (Bind Abst) u1)
                                   .∀c2:C
                                     .csuba g c1 c2
                                       →(or
                                            ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                            ex4_3
                                              C
                                              T
                                              A
                                              λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                              λd2:C.λ:T.λ:A.csuba g d1 d2
                                              λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                              λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                         by (previous . H3 H4)
                         we proved 
                            ∀c2:C
                              .csuba g c1 c2
                                →(or
                                     ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                     ex4_3
                                       C
                                       T
                                       A
                                       λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                       λd2:C.λ:T.λ:A.csuba g d1 d2
                                       λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                       λd2:C.λu2:T.λa:A.arity g d2 u2 a)

                         ∀H3:drop i O c1 (CHead x0 k t)
                           .∀H4:clear (CHead x0 k t) (CHead d1 (Bind Abst) u1)
                             .∀c2:C
                               .csuba g c1 c2
                                 →(or
                                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                      ex4_3
                                        C
                                        T
                                        A
                                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                        λd2:C.λ:T.λ:A.csuba g d1 d2
                                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                        λd2:C.λu2:T.λa:A.arity g d2 u2 a)
                   by (previous . H1 H2)

                      ∀c2:C
                        .csuba g c1 c2
                          →(or
                               ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                               ex4_3
                                 C
                                 T
                                 A
                                 λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                 λd2:C.λ:T.λ:A.csuba g d1 d2
                                 λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                 λd2:C.λu2:T.λa:A.arity g d2 u2 a)
          we proved 
             ∀c2:C
               .csuba g c1 c2
                 →(or
                      ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                      ex4_3
                        C
                        T
                        A
                        λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                        λd2:C.λ:T.λ:A.csuba g d1 d2
                        λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                        λd2:C.λu2:T.λa:A.arity g d2 u2 a)
       we proved 
          ∀g:G
            .∀c1:C
              .∀d1:C
                .∀u1:T
                  .∀i:nat
                    .getl i c1 (CHead d1 (Bind Abst) u1)
                      →∀c2:C
                           .csuba g c1 c2
                             →(or
                                  ex2 C λd2:C.getl i c2 (CHead d2 (Bind Abst) u1) λd2:C.csuba g d1 d2
                                  ex4_3
                                    C
                                    T
                                    A
                                    λd2:C.λu2:T.λ:A.getl i c2 (CHead d2 (Bind Abbr) u2)
                                    λd2:C.λ:T.λ:A.csuba g d1 d2
                                    λ:C.λ:T.λa:A.arity g d1 u1 (asucc g a)
                                    λd2:C.λu2:T.λa:A.arity g d2 u2 a)