DEFINITION sty0_gen_bind()
TYPE =
       ∀g:G
         .∀b:B
           .∀c:C
             .∀u:T
               .∀t1:T
                 .∀x:T
                   .sty0 g c (THead (Bind b) u t1) x
                     →ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2)
BODY =
        assume g: G
        assume b: B
        assume c: C
        assume u: T
        assume t1: T
        assume x: T
        suppose H: sty0 g c (THead (Bind b) u t1) x
           assume y: T
           suppose H0: sty0 g c y x
             we proceed by induction on H0 to prove 
                eq T y (THead (Bind b) u t1)
                  →ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2)
                case sty0_sort : c0:C n:nat ⇒
                   the thesis becomes 
                   ∀H1:eq T (TSort n) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                       λt2:T.eq T (TSort (next g n)) (THead (Bind b) u t2)
                      suppose H1: eq T (TSort n) (THead (Bind b) u t1)
                         (H2) 
                            we proceed by induction on H1 to prove 
                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒True
                                 | TLRef ⇒False
                                 | THead   ⇒False
                               case refl_equal : ⇒
                                  the thesis becomes 
                                  <λ:T.Prop>
                                    CASE TSort n OF
                                      TSort ⇒True
                                    | TLRef ⇒False
                                    | THead   ⇒False
                                     consider I
                                     we proved True

                                        <λ:T.Prop>
                                          CASE TSort n OF
                                            TSort ⇒True
                                          | TLRef ⇒False
                                          | THead   ⇒False

                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒True
                                 | TLRef ⇒False
                                 | THead   ⇒False
                         end of H2
                         consider H2
                         we proved 
                            <λ:T.Prop>
                              CASE THead (Bind b) u t1 OF
                                TSort ⇒True
                              | TLRef ⇒False
                              | THead   ⇒False
                         that is equivalent to False
                         we proceed by induction on the previous result to prove 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (TSort (next g n)) (THead (Bind b) u t2)
                         we proved 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (TSort (next g n)) (THead (Bind b) u t2)

                         ∀H1:eq T (TSort n) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                             λt2:T.eq T (TSort (next g n)) (THead (Bind b) u t2)
                case sty0_abbr : c0:C d:C v:T i:nat :getl i c0 (CHead d (Bind Abbr) v) w:T :sty0 g d v w ⇒
                   the thesis becomes 
                   ∀H4:eq T (TLRef i) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                       λt2:T.eq T (lift (S i) O w) (THead (Bind b) u t2)
                   () by induction hypothesis we know 
                      eq T v (THead (Bind b) u t1)
                        →ex2 T λt2:T.sty0 g (CHead d (Bind b) u) t1 t2 λt2:T.eq T w (THead (Bind b) u t2)
                      suppose H4: eq T (TLRef i) (THead (Bind b) u t1)
                         (H5) 
                            we proceed by induction on H4 to prove 
                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒True
                                 | THead   ⇒False
                               case refl_equal : ⇒
                                  the thesis becomes 
                                  <λ:T.Prop>
                                    CASE TLRef i OF
                                      TSort ⇒False
                                    | TLRef ⇒True
                                    | THead   ⇒False
                                     consider I
                                     we proved True

                                        <λ:T.Prop>
                                          CASE TLRef i OF
                                            TSort ⇒False
                                          | TLRef ⇒True
                                          | THead   ⇒False

                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒True
                                 | THead   ⇒False
                         end of H5
                         consider H5
                         we proved 
                            <λ:T.Prop>
                              CASE THead (Bind b) u t1 OF
                                TSort ⇒False
                              | TLRef ⇒True
                              | THead   ⇒False
                         that is equivalent to False
                         we proceed by induction on the previous result to prove 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (lift (S i) O w) (THead (Bind b) u t2)
                         we proved 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (lift (S i) O w) (THead (Bind b) u t2)

                         ∀H4:eq T (TLRef i) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                             λt2:T.eq T (lift (S i) O w) (THead (Bind b) u t2)
                case sty0_abst : c0:C d:C v:T i:nat :getl i c0 (CHead d (Bind Abst) v) w:T :sty0 g d v w ⇒
                   the thesis becomes 
                   ∀H4:eq T (TLRef i) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                       λt2:T.eq T (lift (S i) O v) (THead (Bind b) u t2)
                   () by induction hypothesis we know 
                      eq T v (THead (Bind b) u t1)
                        →ex2 T λt2:T.sty0 g (CHead d (Bind b) u) t1 t2 λt2:T.eq T w (THead (Bind b) u t2)
                      suppose H4: eq T (TLRef i) (THead (Bind b) u t1)
                         (H5) 
                            we proceed by induction on H4 to prove 
                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒True
                                 | THead   ⇒False
                               case refl_equal : ⇒
                                  the thesis becomes 
                                  <λ:T.Prop>
                                    CASE TLRef i OF
                                      TSort ⇒False
                                    | TLRef ⇒True
                                    | THead   ⇒False
                                     consider I
                                     we proved True

                                        <λ:T.Prop>
                                          CASE TLRef i OF
                                            TSort ⇒False
                                          | TLRef ⇒True
                                          | THead   ⇒False

                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒True
                                 | THead   ⇒False
                         end of H5
                         consider H5
                         we proved 
                            <λ:T.Prop>
                              CASE THead (Bind b) u t1 OF
                                TSort ⇒False
                              | TLRef ⇒True
                              | THead   ⇒False
                         that is equivalent to False
                         we proceed by induction on the previous result to prove 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (lift (S i) O v) (THead (Bind b) u t2)
                         we proved 
                            ex2
                              T
                              λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                              λt2:T.eq T (lift (S i) O v) (THead (Bind b) u t2)

                         ∀H4:eq T (TLRef i) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2
                             λt2:T.eq T (lift (S i) O v) (THead (Bind b) u t2)
                case sty0_bind : b0:B c0:C v:T t0:T t2:T H1:sty0 g (CHead c0 (Bind b0) v) t0 t2 ⇒
                   the thesis becomes 
                   ∀H3:eq T (THead (Bind b0) v t0) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                       λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3)
                   (H2) by induction hypothesis we know 
                      eq T t0 (THead (Bind b) u t1)
                        →(ex2
                             T
                             λt3:T.sty0 g (CHead (CHead c0 (Bind b0) v) (Bind b) u) t1 t3
                             λt3:T.eq T t2 (THead (Bind b) u t3))
                      suppose H3: eq T (THead (Bind b0) v t0) (THead (Bind b) u t1)
                         (H4) 
                            by (f_equal . . . . . H3)
                            we proved 
                               eq
                                 B
                                 <λ:T.B>
                                   CASE THead (Bind b0) v t0 OF
                                     TSort ⇒b0
                                   | TLRef ⇒b0
                                   | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0
                                 <λ:T.B>
                                   CASE THead (Bind b) u t1 OF
                                     TSort ⇒b0
                                   | TLRef ⇒b0
                                   | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0

                               eq
                                 B
                                 λe:T
                                     .<λ:T.B>
                                       CASE e OF
                                         TSort ⇒b0
                                       | TLRef ⇒b0
                                       | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0
                                   THead (Bind b0) v t0
                                 λe:T
                                     .<λ:T.B>
                                       CASE e OF
                                         TSort ⇒b0
                                       | TLRef ⇒b0
                                       | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0
                                   THead (Bind b) u t1
                         end of H4
                         (h1) 
                            (H5) 
                               by (f_equal . . . . . H3)
                               we proved 
                                  eq
                                    T
                                    <λ:T.T> CASE THead (Bind b0) v t0 OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t
                                    <λ:T.T> CASE THead (Bind b) u t1 OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t

                                  eq
                                    T
                                    λe:T.<λ:T.T> CASE e OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t
                                      THead (Bind b0) v t0
                                    λe:T.<λ:T.T> CASE e OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t
                                      THead (Bind b) u t1
                            end of H5
                            (h1) 
                               (H6) 
                                  by (f_equal . . . . . H3)
                                  we proved 
                                     eq
                                       T
                                       <λ:T.T> CASE THead (Bind b0) v t0 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                       <λ:T.T> CASE THead (Bind b) u t1 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t

                                     eq
                                       T
                                       λe:T.<λ:T.T> CASE e OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                         THead (Bind b0) v t0
                                       λe:T.<λ:T.T> CASE e OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                         THead (Bind b) u t1
                               end of H6
                                suppose H7: eq T v u
                                suppose H8: eq B b0 b
                                  (H9) 
                                     consider H6
                                     we proved 
                                        eq
                                          T
                                          <λ:T.T> CASE THead (Bind b0) v t0 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                          <λ:T.T> CASE THead (Bind b) u t1 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                     that is equivalent to eq T t0 t1
                                     we proceed by induction on the previous result to prove 
                                        eq T t1 (THead (Bind b) u t1)
                                          →(ex2
                                               T
                                               λt3:T.sty0 g (CHead (CHead c0 (Bind b0) v) (Bind b) u) t1 t3
                                               λt3:T.eq T t2 (THead (Bind b) u t3))
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H2

                                        eq T t1 (THead (Bind b) u t1)
                                          →(ex2
                                               T
                                               λt3:T.sty0 g (CHead (CHead c0 (Bind b0) v) (Bind b) u) t1 t3
                                               λt3:T.eq T t2 (THead (Bind b) u t3))
                                  end of H9
                                  (H10) 
                                     consider H6
                                     we proved 
                                        eq
                                          T
                                          <λ:T.T> CASE THead (Bind b0) v t0 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                          <λ:T.T> CASE THead (Bind b) u t1 OF TSort ⇒t0 | TLRef ⇒t0 | THead   t⇒t
                                     that is equivalent to eq T t0 t1
                                     we proceed by induction on the previous result to prove sty0 g (CHead c0 (Bind b0) v) t1 t2
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H1
sty0 g (CHead c0 (Bind b0) v) t1 t2
                                  end of H10
                                  (H11) 
                                     we proceed by induction on H7 to prove 
                                        eq T t1 (THead (Bind b) u t1)
                                          →(ex2
                                               T
                                               λt3:T.sty0 g (CHead (CHead c0 (Bind b0) u) (Bind b) u) t1 t3
                                               λt3:T.eq T t2 (THead (Bind b) u t3))
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H9

                                        eq T t1 (THead (Bind b) u t1)
                                          →(ex2
                                               T
                                               λt3:T.sty0 g (CHead (CHead c0 (Bind b0) u) (Bind b) u) t1 t3
                                               λt3:T.eq T t2 (THead (Bind b) u t3))
                                  end of H11
                                  (H12) 
                                     we proceed by induction on H7 to prove sty0 g (CHead c0 (Bind b0) u) t1 t2
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H10
sty0 g (CHead c0 (Bind b0) u) t1 t2
                                  end of H12
                                  (H14) 
                                     we proceed by induction on H8 to prove sty0 g (CHead c0 (Bind b) u) t1 t2
                                        case refl_equal : ⇒
                                           the thesis becomes the hypothesis H12
sty0 g (CHead c0 (Bind b) u) t1 t2
                                  end of H14
                                  by (refl_equal . .)
                                  we proved eq T (THead (Bind b) u t2) (THead (Bind b) u t2)
                                  by (ex_intro2 . . . . H14 previous)
                                  we proved 
                                     ex2
                                       T
                                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                                       λt3:T.eq T (THead (Bind b) u t2) (THead (Bind b) u t3)
                                  by (eq_ind_r . . . previous . H8)
                                  we proved 
                                     ex2
                                       T
                                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                                       λt3:T.eq T (THead (Bind b0) u t2) (THead (Bind b) u t3)
                                  by (eq_ind_r . . . previous . H7)
                                  we proved 
                                     ex2
                                       T
                                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                                       λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3)

                                  eq T v u
                                    →(eq B b0 b
                                         →(ex2
                                              T
                                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                                              λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3)))
                            end of h1
                            (h2) 
                               consider H5
                               we proved 
                                  eq
                                    T
                                    <λ:T.T> CASE THead (Bind b0) v t0 OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t
                                    <λ:T.T> CASE THead (Bind b) u t1 OF TSort ⇒v | TLRef ⇒v | THead  t ⇒t
eq T v u
                            end of h2
                            by (h1 h2)

                               eq B b0 b
                                 →(ex2
                                      T
                                      λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                                      λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3))
                         end of h1
                         (h2) 
                            consider H4
                            we proved 
                               eq
                                 B
                                 <λ:T.B>
                                   CASE THead (Bind b0) v t0 OF
                                     TSort ⇒b0
                                   | TLRef ⇒b0
                                   | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0
                                 <λ:T.B>
                                   CASE THead (Bind b) u t1 OF
                                     TSort ⇒b0
                                   | TLRef ⇒b0
                                   | THead k  ⇒<λ:K.B> CASE k OF Bind b1⇒b1 | Flat ⇒b0
eq B b0 b
                         end of h2
                         by (h1 h2)
                         we proved 
                            ex2
                              T
                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                              λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3)

                         ∀H3:eq T (THead (Bind b0) v t0) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                             λt3:T.eq T (THead (Bind b0) v t2) (THead (Bind b) u t3)
                case sty0_appl : c0:C v:T t0:T t2:T :sty0 g c0 t0 t2 ⇒
                   the thesis becomes 
                   ∀H3:eq T (THead (Flat Appl) v t0) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                       λt3:T.eq T (THead (Flat Appl) v t2) (THead (Bind b) u t3)
                   () by induction hypothesis we know 
                      eq T t0 (THead (Bind b) u t1)
                        →ex2 T λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3 λt3:T.eq T t2 (THead (Bind b) u t3)
                      suppose H3: eq T (THead (Flat Appl) v t0) (THead (Bind b) u t1)
                         (H4) 
                            we proceed by induction on H3 to prove 
                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒False
                                 | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                               case refl_equal : ⇒
                                  the thesis becomes 
                                  <λ:T.Prop>
                                    CASE THead (Flat Appl) v t0 OF
                                      TSort ⇒False
                                    | TLRef ⇒False
                                    | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                                     consider I
                                     we proved True

                                        <λ:T.Prop>
                                          CASE THead (Flat Appl) v t0 OF
                                            TSort ⇒False
                                          | TLRef ⇒False
                                          | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True

                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒False
                                 | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                         end of H4
                         consider H4
                         we proved 
                            <λ:T.Prop>
                              CASE THead (Bind b) u t1 OF
                                TSort ⇒False
                              | TLRef ⇒False
                              | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                         that is equivalent to False
                         we proceed by induction on the previous result to prove 
                            ex2
                              T
                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                              λt3:T.eq T (THead (Flat Appl) v t2) (THead (Bind b) u t3)
                         we proved 
                            ex2
                              T
                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                              λt3:T.eq T (THead (Flat Appl) v t2) (THead (Bind b) u t3)

                         ∀H3:eq T (THead (Flat Appl) v t0) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                             λt3:T.eq T (THead (Flat Appl) v t2) (THead (Bind b) u t3)
                case sty0_cast : c0:C v1:T v2:T :sty0 g c0 v1 v2 t0:T t2:T :sty0 g c0 t0 t2 ⇒
                   the thesis becomes 
                   ∀H5:eq T (THead (Flat Cast) v1 t0) (THead (Bind b) u t1)
                     .ex2
                       T
                       λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                       λt3:T.eq T (THead (Flat Cast) v2 t2) (THead (Bind b) u t3)
                   () by induction hypothesis we know 
                      eq T v1 (THead (Bind b) u t1)
                        →ex2 T λt2:T.sty0 g (CHead c0 (Bind b) u) t1 t2 λt2:T.eq T v2 (THead (Bind b) u t2)
                   () by induction hypothesis we know 
                      eq T t0 (THead (Bind b) u t1)
                        →ex2 T λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3 λt3:T.eq T t2 (THead (Bind b) u t3)
                      suppose H5: eq T (THead (Flat Cast) v1 t0) (THead (Bind b) u t1)
                         (H6) 
                            we proceed by induction on H5 to prove 
                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒False
                                 | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                               case refl_equal : ⇒
                                  the thesis becomes 
                                  <λ:T.Prop>
                                    CASE THead (Flat Cast) v1 t0 OF
                                      TSort ⇒False
                                    | TLRef ⇒False
                                    | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                                     consider I
                                     we proved True

                                        <λ:T.Prop>
                                          CASE THead (Flat Cast) v1 t0 OF
                                            TSort ⇒False
                                          | TLRef ⇒False
                                          | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True

                               <λ:T.Prop>
                                 CASE THead (Bind b) u t1 OF
                                   TSort ⇒False
                                 | TLRef ⇒False
                                 | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                         end of H6
                         consider H6
                         we proved 
                            <λ:T.Prop>
                              CASE THead (Bind b) u t1 OF
                                TSort ⇒False
                              | TLRef ⇒False
                              | THead k  ⇒<λ:K.Prop> CASE k OF Bind ⇒False | Flat ⇒True
                         that is equivalent to False
                         we proceed by induction on the previous result to prove 
                            ex2
                              T
                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                              λt3:T.eq T (THead (Flat Cast) v2 t2) (THead (Bind b) u t3)
                         we proved 
                            ex2
                              T
                              λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                              λt3:T.eq T (THead (Flat Cast) v2 t2) (THead (Bind b) u t3)

                         ∀H5:eq T (THead (Flat Cast) v1 t0) (THead (Bind b) u t1)
                           .ex2
                             T
                             λt3:T.sty0 g (CHead c0 (Bind b) u) t1 t3
                             λt3:T.eq T (THead (Flat Cast) v2 t2) (THead (Bind b) u t3)
             we proved 
                eq T y (THead (Bind b) u t1)
                  →ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2)
          we proved 
             ∀y:T
               .sty0 g c y x
                 →(eq T y (THead (Bind b) u t1)
                      →ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2))
          by (insert_eq . . . . previous H)
          we proved ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2)
       we proved 
          ∀g:G
            .∀b:B
              .∀c:C
                .∀u:T
                  .∀t1:T
                    .∀x:T
                      .sty0 g c (THead (Bind b) u t1) x
                        →ex2 T λt2:T.sty0 g (CHead c (Bind b) u) t1 t2 λt2:T.eq T x (THead (Bind b) u t2)