DEFINITION csuba_gen_bind_rev()
TYPE =
       ∀g:G
         .∀b1:B
           .∀e1:C
             .∀c2:C
               .∀v1:T
                 .csuba g c2 (CHead e1 (Bind b1) v1)
                   →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
BODY =
        assume g: G
        assume b1: B
        assume e1: C
        assume c2: C
        assume v1: T
        suppose H: csuba g c2 (CHead e1 (Bind b1) v1)
           assume y: C
           suppose H0: csuba g c2 y
             we proceed by induction on H0 to prove 
                eq C y (CHead e1 (Bind b1) v1)
                  →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                case csuba_sort : n:nat ⇒
                   the thesis becomes 
                   ∀H1:eq C (CSort n) (CHead e1 (Bind b1) v1)
                     .ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CSort n) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                      suppose H1: eq C (CSort n) (CHead e1 (Bind b1) v1)
                         (H2) 
                            we proceed by induction on H1 to prove <λ:C.Prop> CASE CHead e1 (Bind b1) v1 OF CSort ⇒True | CHead   ⇒False
                               case refl_equal : ⇒
                                  the thesis becomes <λ:C.Prop> CASE CSort n OF CSort ⇒True | CHead   ⇒False
                                     consider I
                                     we proved True
<λ:C.Prop> CASE CSort n OF CSort ⇒True | CHead   ⇒False
<λ:C.Prop> CASE CHead e1 (Bind b1) v1 OF CSort ⇒True | CHead   ⇒False
                         end of H2
                         consider H2
                         we proved <λ:C.Prop> CASE CHead e1 (Bind b1) v1 OF CSort ⇒True | CHead   ⇒False
                         that is equivalent to False
                         we proceed by induction on the previous result to prove ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CSort n) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                         we proved ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CSort n) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1

                         ∀H1:eq C (CSort n) (CHead e1 (Bind b1) v1)
                           .ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CSort n) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                case csuba_head : c1:C c3:C H1:csuba g c1 c3 k:K u:T ⇒
                   the thesis becomes 
                   ∀H3:eq C (CHead c3 k u) (CHead e1 (Bind b1) v1)
                     .ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                   (H2) by induction hypothesis we know 
                      eq C c3 (CHead e1 (Bind b1) v1)
                        →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c1 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                      suppose H3: eq C (CHead c3 k u) (CHead e1 (Bind b1) v1)
                         (H4) 
                            by (f_equal . . . . . H3)
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 k u OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c

                               eq
                                 C
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead c3 k u)
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead e1 (Bind b1) v1)
                         end of H4
                         (h1) 
                            (H5) 
                               by (f_equal . . . . . H3)
                               we proved 
                                  eq
                                    K
                                    <λ:C.K> CASE CHead c3 k u OF CSort ⇒k | CHead  k0 ⇒k0
                                    <λ:C.K> CASE CHead e1 (Bind b1) v1 OF CSort ⇒k | CHead  k0 ⇒k0

                                  eq
                                    K
                                    λe:C.<λ:C.K> CASE e OF CSort ⇒k | CHead  k0 ⇒k0 (CHead c3 k u)
                                    λe:C.<λ:C.K> CASE e OF CSort ⇒k | CHead  k0 ⇒k0 (CHead e1 (Bind b1) v1)
                            end of H5
                            (h1) 
                               (H6) 
                                  by (f_equal . . . . . H3)
                                  we proved 
                                     eq
                                       T
                                       <λ:C.T> CASE CHead c3 k u OF CSort ⇒u | CHead   t⇒t
                                       <λ:C.T> CASE CHead e1 (Bind b1) v1 OF CSort ⇒u | CHead   t⇒t

                                     eq
                                       T
                                       λe:C.<λ:C.T> CASE e OF CSort ⇒u | CHead   t⇒t (CHead c3 k u)
                                       λe:C.<λ:C.T> CASE e OF CSort ⇒u | CHead   t⇒t (CHead e1 (Bind b1) v1)
                               end of H6
                                suppose H7: eq K k (Bind b1)
                                suppose H8: eq C c3 e1
                                  (h1) 
                                     (H10) 
                                        we proceed by induction on H8 to prove csuba g c1 e1
                                           case refl_equal : ⇒
                                              the thesis becomes the hypothesis H1
csuba g c1 e1
                                     end of H10
                                     by (refl_equal . .)
                                     we proved eq C (CHead c1 (Bind b1) v1) (CHead c1 (Bind b1) v1)
                                     by (ex2_3_intro . . . . . . . . previous H10)
                                     we proved 
                                        ex2_3
                                          B
                                          C
                                          T
                                          λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind b1) v1) (CHead e2 (Bind b2) v2)
                                          λ:B.λe2:C.λ:T.csuba g e2 e1
                                     by (eq_ind_r . . . previous . H7)
ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k v1) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                                  end of h1
                                  (h2) 
                                     consider H6
                                     we proved 
                                        eq
                                          T
                                          <λ:C.T> CASE CHead c3 k u OF CSort ⇒u | CHead   t⇒t
                                          <λ:C.T> CASE CHead e1 (Bind b1) v1 OF CSort ⇒u | CHead   t⇒t
eq T u v1
                                  end of h2
                                  by (eq_ind_r . . . h1 . h2)
                                  we proved ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1

                                  eq K k (Bind b1)
                                    →(eq C c3 e1
                                         →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1)
                            end of h1
                            (h2) 
                               consider H5
                               we proved 
                                  eq
                                    K
                                    <λ:C.K> CASE CHead c3 k u OF CSort ⇒k | CHead  k0 ⇒k0
                                    <λ:C.K> CASE CHead e1 (Bind b1) v1 OF CSort ⇒k | CHead  k0 ⇒k0
eq K k (Bind b1)
                            end of h2
                            by (h1 h2)

                               eq C c3 e1
                                 →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                         end of h1
                         (h2) 
                            consider H4
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 k u OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c
eq C c3 e1
                         end of h2
                         by (h1 h2)
                         we proved ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1

                         ∀H3:eq C (CHead c3 k u) (CHead e1 (Bind b1) v1)
                           .ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C (CHead c1 k u) (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                case csuba_void : c1:C c3:C H1:csuba g c1 c3 b:B H3:not (eq B b Void) u1:T u2:T ⇒
                   the thesis becomes 
                   ∀H4:eq C (CHead c3 (Bind b) u2) (CHead e1 (Bind b1) v1)
                     .ex2_3
                       B
                       C
                       T
                       λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Void) u1) (CHead e2 (Bind b2) v2)
                       λ:B.λe2:C.λ:T.csuba g e2 e1
                   (H2) by induction hypothesis we know 
                      eq C c3 (CHead e1 (Bind b1) v1)
                        →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c1 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                      suppose H4: eq C (CHead c3 (Bind b) u2) (CHead e1 (Bind b1) v1)
                         (H5) 
                            by (f_equal . . . . . H4)
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 (Bind b) u2 OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c

                               eq
                                 C
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead c3 (Bind b) u2)
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead e1 (Bind b1) v1)
                         end of H5
                         (h1) 
                            (H6) 
                               by (f_equal . . . . . H4)
                               we proved 
                                  eq
                                    B
                                    <λ:C.B>
                                      CASE CHead c3 (Bind b) u2 OF
                                        CSort ⇒b
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b
                                    <λ:C.B>
                                      CASE CHead e1 (Bind b1) v1 OF
                                        CSort ⇒b
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b

                                  eq
                                    B
                                    λe:C.<λ:C.B> CASE e OF CSort ⇒b | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b
                                      CHead c3 (Bind b) u2
                                    λe:C.<λ:C.B> CASE e OF CSort ⇒b | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b
                                      CHead e1 (Bind b1) v1
                            end of H6
                            (H8) 
                               consider H6
                               we proved 
                                  eq
                                    B
                                    <λ:C.B>
                                      CASE CHead c3 (Bind b) u2 OF
                                        CSort ⇒b
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b
                                    <λ:C.B>
                                      CASE CHead e1 (Bind b1) v1 OF
                                        CSort ⇒b
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b0⇒b0 | Flat ⇒b
eq B b b1
                            end of H8
                            suppose H9: eq C c3 e1
                               (H12) 
                                  we proceed by induction on H9 to prove csuba g c1 e1
                                     case refl_equal : ⇒
                                        the thesis becomes the hypothesis H1
csuba g c1 e1
                               end of H12
                               by (refl_equal . .)
                               we proved eq C (CHead c1 (Bind Void) u1) (CHead c1 (Bind Void) u1)
                               by (ex2_3_intro . . . . . . . . previous H12)
                               we proved 
                                  ex2_3
                                    B
                                    C
                                    T
                                    λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Void) u1) (CHead e2 (Bind b2) v2)
                                    λ:B.λe2:C.λ:T.csuba g e2 e1

                               eq C c3 e1
                                 →(ex2_3
                                      B
                                      C
                                      T
                                      λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Void) u1) (CHead e2 (Bind b2) v2)
                                      λ:B.λe2:C.λ:T.csuba g e2 e1)
                         end of h1
                         (h2) 
                            consider H5
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 (Bind b) u2 OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c
eq C c3 e1
                         end of h2
                         by (h1 h2)
                         we proved 
                            ex2_3
                              B
                              C
                              T
                              λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Void) u1) (CHead e2 (Bind b2) v2)
                              λ:B.λe2:C.λ:T.csuba g e2 e1

                         ∀H4:eq C (CHead c3 (Bind b) u2) (CHead e1 (Bind b1) v1)
                           .ex2_3
                             B
                             C
                             T
                             λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Void) u1) (CHead e2 (Bind b2) v2)
                             λ:B.λe2:C.λ:T.csuba g e2 e1
                case csuba_abst : c1:C c3:C H1:csuba g c1 c3 t:T a:A :arity g c1 t (asucc g a) u:T H4:arity g c3 u a ⇒
                   the thesis becomes 
                   ∀H5:eq C (CHead c3 (Bind Abbr) u) (CHead e1 (Bind b1) v1)
                     .ex2_3
                       B
                       C
                       T
                       λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                       λ:B.λe2:C.λ:T.csuba g e2 e1
                   (H2) by induction hypothesis we know 
                      eq C c3 (CHead e1 (Bind b1) v1)
                        →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c1 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                      suppose H5: eq C (CHead c3 (Bind Abbr) u) (CHead e1 (Bind b1) v1)
                         (H6) 
                            by (f_equal . . . . . H5)
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 (Bind Abbr) u OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c

                               eq
                                 C
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead c3 (Bind Abbr) u)
                                 λe:C.<λ:C.C> CASE e OF CSort ⇒c3 | CHead c  ⇒c (CHead e1 (Bind b1) v1)
                         end of H6
                         (h1) 
                            (H7) 
                               by (f_equal . . . . . H5)
                               we proved 
                                  eq
                                    B
                                    <λ:C.B>
                                      CASE CHead c3 (Bind Abbr) u OF
                                        CSort ⇒Abbr
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr
                                    <λ:C.B>
                                      CASE CHead e1 (Bind b1) v1 OF
                                        CSort ⇒Abbr
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr

                                  eq
                                    B
                                    λe:C
                                        .<λ:C.B>
                                          CASE e OF
                                            CSort ⇒Abbr
                                          | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr
                                      CHead c3 (Bind Abbr) u
                                    λe:C
                                        .<λ:C.B>
                                          CASE e OF
                                            CSort ⇒Abbr
                                          | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr
                                      CHead e1 (Bind b1) v1
                            end of H7
                            (h1) 
                               (H8) 
                                  by (f_equal . . . . . H5)
                                  we proved 
                                     eq
                                       T
                                       <λ:C.T> CASE CHead c3 (Bind Abbr) u OF CSort ⇒u | CHead   t0⇒t0
                                       <λ:C.T> CASE CHead e1 (Bind b1) v1 OF CSort ⇒u | CHead   t0⇒t0

                                     eq
                                       T
                                       λe:C.<λ:C.T> CASE e OF CSort ⇒u | CHead   t0⇒t0 (CHead c3 (Bind Abbr) u)
                                       λe:C.<λ:C.T> CASE e OF CSort ⇒u | CHead   t0⇒t0 (CHead e1 (Bind b1) v1)
                               end of H8
                                suppose H9: eq B Abbr b1
                                suppose H10: eq C c3 e1
                                  (H11) 
                                     consider H8
                                     we proved 
                                        eq
                                          T
                                          <λ:C.T> CASE CHead c3 (Bind Abbr) u OF CSort ⇒u | CHead   t0⇒t0
                                          <λ:C.T> CASE CHead e1 (Bind b1) v1 OF CSort ⇒u | CHead   t0⇒t0
                                     that is equivalent to eq T u v1
                                     we proceed by induction on the previous result to prove arity g c3 v1 a
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H4
arity g c3 v1 a
                                  end of H11
                                  (H13) 
                                     we proceed by induction on H10 to prove 
                                        eq C e1 (CHead e1 (Bind b1) v1)
                                          →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c1 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H2

                                        eq C e1 (CHead e1 (Bind b1) v1)
                                          →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c1 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
                                  end of H13
                                  (H14) 
                                     we proceed by induction on H10 to prove csuba g c1 e1
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H1
csuba g c1 e1
                                  end of H14
                                  by (refl_equal . .)
                                  we proved eq C (CHead c1 (Bind Abst) t) (CHead c1 (Bind Abst) t)
                                  by (ex2_3_intro . . . . . . . . previous H14)
                                  we proved 
                                     ex2_3
                                       B
                                       C
                                       T
                                       λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                                       λ:B.λe2:C.λ:T.csuba g e2 e1

                                  eq B Abbr b1
                                    →(eq C c3 e1
                                         →(ex2_3
                                              B
                                              C
                                              T
                                              λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                                              λ:B.λe2:C.λ:T.csuba g e2 e1))
                            end of h1
                            (h2) 
                               consider H7
                               we proved 
                                  eq
                                    B
                                    <λ:C.B>
                                      CASE CHead c3 (Bind Abbr) u OF
                                        CSort ⇒Abbr
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr
                                    <λ:C.B>
                                      CASE CHead e1 (Bind b1) v1 OF
                                        CSort ⇒Abbr
                                      | CHead  k ⇒<λ:K.B> CASE k OF Bind b⇒b | Flat ⇒Abbr
eq B Abbr b1
                            end of h2
                            by (h1 h2)

                               eq C c3 e1
                                 →(ex2_3
                                      B
                                      C
                                      T
                                      λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                                      λ:B.λe2:C.λ:T.csuba g e2 e1)
                         end of h1
                         (h2) 
                            consider H6
                            we proved 
                               eq
                                 C
                                 <λ:C.C> CASE CHead c3 (Bind Abbr) u OF CSort ⇒c3 | CHead c  ⇒c
                                 <λ:C.C> CASE CHead e1 (Bind b1) v1 OF CSort ⇒c3 | CHead c  ⇒c
eq C c3 e1
                         end of h2
                         by (h1 h2)
                         we proved 
                            ex2_3
                              B
                              C
                              T
                              λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                              λ:B.λe2:C.λ:T.csuba g e2 e1

                         ∀H5:eq C (CHead c3 (Bind Abbr) u) (CHead e1 (Bind b1) v1)
                           .ex2_3
                             B
                             C
                             T
                             λb2:B.λe2:C.λv2:T.eq C (CHead c1 (Bind Abst) t) (CHead e2 (Bind b2) v2)
                             λ:B.λe2:C.λ:T.csuba g e2 e1
             we proved 
                eq C y (CHead e1 (Bind b1) v1)
                  →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
          we proved 
             ∀y:C
               .csuba g c2 y
                 →(eq C y (CHead e1 (Bind b1) v1)
                      →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1)
          by (insert_eq . . . . previous H)
          we proved ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1
       we proved 
          ∀g:G
            .∀b1:B
              .∀e1:C
                .∀c2:C
                  .∀v1:T
                    .csuba g c2 (CHead e1 (Bind b1) v1)
                      →ex2_3 B C T λb2:B.λe2:C.λv2:T.eq C c2 (CHead e2 (Bind b2) v2) λ:B.λe2:C.λ:T.csuba g e2 e1