DEFINITION pc3_gen_not_abst()
TYPE =
       ∀b:B
         .not (eq B b Abst)
           →∀c:C
                .∀t1:T
                  .∀t2:T
                    .∀u1:T
                      .∀u2:T
                        .pc3 c (THead (Bind b) u1 t1) (THead (Bind Abst) u2 t2)
                          →pc3 (CHead c (Bind b) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
BODY =
       assume b: B
          we proceed by induction on b to prove 
             not (eq B b Abst)
               →∀c:C
                    .∀t1:T
                      .∀t2:T
                        .∀u1:T
                          .∀u2:T
                            .pc3 c (THead (Bind b) u1 t1) (THead (Bind Abst) u2 t2)
                              →pc3 (CHead c (Bind b) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
             case Abbr : ⇒
                the thesis becomes 
                not (eq B Abbr Abst)
                  →∀c:C
                       .∀t1:T
                         .∀t2:T
                           .∀u1:T
                             .∀u2:T
                               .pc3 c (THead (Bind Abbr) u1 t1) (THead (Bind Abst) u2 t2)
                                 →pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                    suppose : not (eq B Abbr Abst)
                    assume c: C
                    assume t1: T
                    assume t2: T
                    assume u1: T
                    assume u2: T
                    suppose H0: pc3 c (THead (Bind Abbr) u1 t1) (THead (Bind Abst) u2 t2)
                      (H1) consider H0
                      consider H1
                      we proved pc3 c (THead (Bind Abbr) u1 t1) (THead (Bind Abst) u2 t2)
                      that is equivalent to 
                         ex2
                           T
                           λt:T.pr3 c (THead (Bind Abbr) u1 t1) t
                           λt:T.pr3 c (THead (Bind Abst) u2 t2) t
                      we proceed by induction on the previous result to prove 
                         pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                         case ex_intro2 : x:T H2:pr3 c (THead (Bind Abbr) u1 t1) x H3:pr3 c (THead (Bind Abst) u2 t2) x ⇒
                            the thesis becomes 
                            pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                               (H4) 
                                  by (pr3_gen_abbr . . . . H2)

                                     or
                                       ex3_2
                                         T
                                         T
                                         λu2:T.λt2:T.eq T x (THead (Bind Abbr) u2 t2)
                                         λu2:T.λ:T.pr3 c u1 u2
                                         λ:T.λt2:T.pr3 (CHead c (Bind Abbr) u1) t1 t2
                                       pr3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O x)
                               end of H4
                               we proceed by induction on H4 to prove 
                                  pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                  case or_introl : H5:ex3_2 T T λu3:T.λt3:T.eq T x (THead (Bind Abbr) u3 t3) λu3:T.λ:T.pr3 c u1 u3 λ:T.λt3:T.pr3 (CHead c (Bind Abbr) u1) t1 t3 ⇒
                                     the thesis becomes 
                                     pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                        we proceed by induction on H5 to prove 
                                           pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                           case ex3_2_intro : x0:T x1:T H6:eq T x (THead (Bind Abbr) x0 x1) :pr3 c u1 x0 :pr3 (CHead c (Bind Abbr) u1) t1 x1 ⇒
                                              the thesis becomes 
                                              pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                 (H9) 
                                                    by (pr3_gen_abst . . . . H3)

                                                       ex3_2
                                                         T
                                                         T
                                                         λu2:T.λt2:T.eq T x (THead (Bind Abst) u2 t2)
                                                         λu2:T.λ:T.pr3 c u2 u2
                                                         λ:T.λt2:T.∀b:B.∀u:T.(pr3 (CHead c (Bind b) u) t2 t2)
                                                 end of H9
                                                 we proceed by induction on H9 to prove 
                                                    pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                    case ex3_2_intro : x2:T x3:T H10:eq T x (THead (Bind Abst) x2 x3) :pr3 c u2 x2 :∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t2 x3) ⇒
                                                       the thesis becomes 
                                                       pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                          (H13) 
                                                             we proceed by induction on H10 to prove eq T (THead (Bind Abst) x2 x3) (THead (Bind Abbr) x0 x1)
                                                                case refl_equal : ⇒
                                                                   the thesis becomes the hypothesis H6
eq T (THead (Bind Abst) x2 x3) (THead (Bind Abbr) x0 x1)
                                                          end of H13
                                                          (H14) 
                                                             we proceed by induction on H13 to prove 
                                                                <λ:T.Prop>
                                                                  CASE THead (Bind Abbr) x0 x1 OF
                                                                    TSort ⇒False
                                                                  | TLRef ⇒False
                                                                  | THead k  ⇒
                                                                        <λ:K.Prop>
                                                                          CASE k OF
                                                                            Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                          | Flat ⇒False
                                                                case refl_equal : ⇒
                                                                   the thesis becomes 
                                                                   <λ:T.Prop>
                                                                     CASE THead (Bind Abst) x2 x3 OF
                                                                       TSort ⇒False
                                                                     | TLRef ⇒False
                                                                     | THead k  ⇒
                                                                           <λ:K.Prop>
                                                                             CASE k OF
                                                                               Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                             | Flat ⇒False
                                                                      consider I
                                                                      we proved True

                                                                         <λ:T.Prop>
                                                                           CASE THead (Bind Abst) x2 x3 OF
                                                                             TSort ⇒False
                                                                           | TLRef ⇒False
                                                                           | THead k  ⇒
                                                                                 <λ:K.Prop>
                                                                                   CASE k OF
                                                                                     Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                                   | Flat ⇒False

                                                                <λ:T.Prop>
                                                                  CASE THead (Bind Abbr) x0 x1 OF
                                                                    TSort ⇒False
                                                                  | TLRef ⇒False
                                                                  | THead k  ⇒
                                                                        <λ:K.Prop>
                                                                          CASE k OF
                                                                            Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                          | Flat ⇒False
                                                          end of H14
                                                          consider H14
                                                          we proved 
                                                             <λ:T.Prop>
                                                               CASE THead (Bind Abbr) x0 x1 OF
                                                                 TSort ⇒False
                                                               | TLRef ⇒False
                                                               | THead k  ⇒
                                                                     <λ:K.Prop>
                                                                       CASE k OF
                                                                         Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                       | Flat ⇒False
                                                          that is equivalent to False
                                                          we proceed by induction on the previous result to prove 
                                                             pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                                             pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                                    pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                           pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                  case or_intror : H5:pr3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O x) ⇒
                                     the thesis becomes 
                                     pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                        (H6) 
                                           by (pr3_gen_abst . . . . H3)

                                              ex3_2
                                                T
                                                T
                                                λu2:T.λt2:T.eq T x (THead (Bind Abst) u2 t2)
                                                λu2:T.λ:T.pr3 c u2 u2
                                                λ:T.λt2:T.∀b:B.∀u:T.(pr3 (CHead c (Bind b) u) t2 t2)
                                        end of H6
                                        we proceed by induction on H6 to prove 
                                           pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                           case ex3_2_intro : x0:T x1:T H7:eq T x (THead (Bind Abst) x0 x1) H8:pr3 c u2 x0 H9:∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t2 x1) ⇒
                                              the thesis becomes 
                                              pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                 (H10) 
                                                    we proceed by induction on H7 to prove 
                                                       pr3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) x0 x1))
                                                       case refl_equal : ⇒
                                                          the thesis becomes the hypothesis H5

                                                       pr3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) x0 x1))
                                                 end of H10
                                                 (h1) 
                                                    by (drop_refl .)
                                                    we proved drop O O c c
                                                    that is equivalent to drop (r (Bind Abbr) O) O c c
                                                    by (drop_drop . . . . previous .)
drop (S O) O (CHead c (Bind Abbr) u1) c
                                                 end of h1
                                                 (h2) 
                                                    by (H9 . .)
                                                    we proved pr3 (CHead c (Bind Abst) x0) t2 x1
                                                    by (pr3_head_12 . . . H8 . . . previous)
pr3 c (THead (Bind Abst) u2 t2) (THead (Bind Abst) x0 x1)
                                                 end of h2
                                                 by (pr3_lift . . . . h1 . . h2)
                                                 we proved 
                                                    pr3
                                                      CHead c (Bind Abbr) u1
                                                      lift (S O) O (THead (Bind Abst) u2 t2)
                                                      lift (S O) O (THead (Bind Abst) x0 x1)
                                                 by (pc3_pr3_t . . . H10 . previous)

                                                    pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                           pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                  pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                      we proved 
                         pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                      not (eq B Abbr Abst)
                        →∀c:C
                             .∀t1:T
                               .∀t2:T
                                 .∀u1:T
                                   .∀u2:T
                                     .pc3 c (THead (Bind Abbr) u1 t1) (THead (Bind Abst) u2 t2)
                                       →pc3 (CHead c (Bind Abbr) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
             case Abst : ⇒
                the thesis becomes 
                not (eq B Abst Abst)
                  →∀c:C
                       .∀t1:T
                         .∀t2:T
                           .∀u1:T
                             .∀u2:T
                               .pc3 c (THead (Bind Abst) u1 t1) (THead (Bind Abst) u2 t2)
                                 →pc3 (CHead c (Bind Abst) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                    suppose H: not (eq B Abst Abst)
                    assume c: C
                    assume t1: T
                    assume t2: T
                    assume u1: T
                    assume u2: T
                    suppose : pc3 c (THead (Bind Abst) u1 t1) (THead (Bind Abst) u2 t2)
                      (H1) 
                         by (refl_equal . .)
                         we proved eq B Abst Abst
                         by (H previous)
                         we proved False
                         by cases on the previous result we prove 
                            pc3 (CHead c (Bind Abst) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                            pc3 (CHead c (Bind Abst) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                      end of H1
                      consider H1
                      we proved 
                         pc3 (CHead c (Bind Abst) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                      not (eq B Abst Abst)
                        →∀c:C
                             .∀t1:T
                               .∀t2:T
                                 .∀u1:T
                                   .∀u2:T
                                     .pc3 c (THead (Bind Abst) u1 t1) (THead (Bind Abst) u2 t2)
                                       →pc3 (CHead c (Bind Abst) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
             case Void : ⇒
                the thesis becomes 
                not (eq B Void Abst)
                  →∀c:C
                       .∀t1:T
                         .∀t2:T
                           .∀u1:T
                             .∀u2:T
                               .pc3 c (THead (Bind Void) u1 t1) (THead (Bind Abst) u2 t2)
                                 →pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                    suppose : not (eq B Void Abst)
                    assume c: C
                    assume t1: T
                    assume t2: T
                    assume u1: T
                    assume u2: T
                    suppose H0: pc3 c (THead (Bind Void) u1 t1) (THead (Bind Abst) u2 t2)
                      (H1) consider H0
                      consider H1
                      we proved pc3 c (THead (Bind Void) u1 t1) (THead (Bind Abst) u2 t2)
                      that is equivalent to 
                         ex2
                           T
                           λt:T.pr3 c (THead (Bind Void) u1 t1) t
                           λt:T.pr3 c (THead (Bind Abst) u2 t2) t
                      we proceed by induction on the previous result to prove 
                         pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                         case ex_intro2 : x:T H2:pr3 c (THead (Bind Void) u1 t1) x H3:pr3 c (THead (Bind Abst) u2 t2) x ⇒
                            the thesis becomes 
                            pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                               (H4) 
                                  by (pr3_gen_void . . . . H2)

                                     or
                                       ex3_2
                                         T
                                         T
                                         λu2:T.λt2:T.eq T x (THead (Bind Void) u2 t2)
                                         λu2:T.λ:T.pr3 c u1 u2
                                         λ:T.λt2:T.∀b:B.∀u:T.(pr3 (CHead c (Bind b) u) t1 t2)
                                       pr3 (CHead c (Bind Void) u1) t1 (lift (S O) O x)
                               end of H4
                               we proceed by induction on H4 to prove 
                                  pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                  case or_introl : H5:ex3_2 T T λu3:T.λt3:T.eq T x (THead (Bind Void) u3 t3) λu3:T.λ:T.pr3 c u1 u3 λ:T.λt3:T.∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t1 t3) ⇒
                                     the thesis becomes 
                                     pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                        we proceed by induction on H5 to prove 
                                           pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                           case ex3_2_intro : x0:T x1:T H6:eq T x (THead (Bind Void) x0 x1) :pr3 c u1 x0 :∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t1 x1) ⇒
                                              the thesis becomes 
                                              pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                 (H9) 
                                                    by (pr3_gen_abst . . . . H3)

                                                       ex3_2
                                                         T
                                                         T
                                                         λu2:T.λt2:T.eq T x (THead (Bind Abst) u2 t2)
                                                         λu2:T.λ:T.pr3 c u2 u2
                                                         λ:T.λt2:T.∀b:B.∀u:T.(pr3 (CHead c (Bind b) u) t2 t2)
                                                 end of H9
                                                 we proceed by induction on H9 to prove 
                                                    pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                    case ex3_2_intro : x2:T x3:T H10:eq T x (THead (Bind Abst) x2 x3) :pr3 c u2 x2 :∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t2 x3) ⇒
                                                       the thesis becomes 
                                                       pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                          (H13) 
                                                             we proceed by induction on H10 to prove eq T (THead (Bind Abst) x2 x3) (THead (Bind Void) x0 x1)
                                                                case refl_equal : ⇒
                                                                   the thesis becomes the hypothesis H6
eq T (THead (Bind Abst) x2 x3) (THead (Bind Void) x0 x1)
                                                          end of H13
                                                          (H14) 
                                                             we proceed by induction on H13 to prove 
                                                                <λ:T.Prop>
                                                                  CASE THead (Bind Void) x0 x1 OF
                                                                    TSort ⇒False
                                                                  | TLRef ⇒False
                                                                  | THead k  ⇒
                                                                        <λ:K.Prop>
                                                                          CASE k OF
                                                                            Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                          | Flat ⇒False
                                                                case refl_equal : ⇒
                                                                   the thesis becomes 
                                                                   <λ:T.Prop>
                                                                     CASE THead (Bind Abst) x2 x3 OF
                                                                       TSort ⇒False
                                                                     | TLRef ⇒False
                                                                     | THead k  ⇒
                                                                           <λ:K.Prop>
                                                                             CASE k OF
                                                                               Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                             | Flat ⇒False
                                                                      consider I
                                                                      we proved True

                                                                         <λ:T.Prop>
                                                                           CASE THead (Bind Abst) x2 x3 OF
                                                                             TSort ⇒False
                                                                           | TLRef ⇒False
                                                                           | THead k  ⇒
                                                                                 <λ:K.Prop>
                                                                                   CASE k OF
                                                                                     Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                                   | Flat ⇒False

                                                                <λ:T.Prop>
                                                                  CASE THead (Bind Void) x0 x1 OF
                                                                    TSort ⇒False
                                                                  | TLRef ⇒False
                                                                  | THead k  ⇒
                                                                        <λ:K.Prop>
                                                                          CASE k OF
                                                                            Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                          | Flat ⇒False
                                                          end of H14
                                                          consider H14
                                                          we proved 
                                                             <λ:T.Prop>
                                                               CASE THead (Bind Void) x0 x1 OF
                                                                 TSort ⇒False
                                                               | TLRef ⇒False
                                                               | THead k  ⇒
                                                                     <λ:K.Prop>
                                                                       CASE k OF
                                                                         Bind b0⇒<λ:B.Prop> CASE b0 OF Abbr⇒False | Abst⇒True | Void⇒False
                                                                       | Flat ⇒False
                                                          that is equivalent to False
                                                          we proceed by induction on the previous result to prove 
                                                             pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                                             pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                                    pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                           pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                  case or_intror : H5:pr3 (CHead c (Bind Void) u1) t1 (lift (S O) O x) ⇒
                                     the thesis becomes 
                                     pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                        (H6) 
                                           by (pr3_gen_abst . . . . H3)

                                              ex3_2
                                                T
                                                T
                                                λu2:T.λt2:T.eq T x (THead (Bind Abst) u2 t2)
                                                λu2:T.λ:T.pr3 c u2 u2
                                                λ:T.λt2:T.∀b:B.∀u:T.(pr3 (CHead c (Bind b) u) t2 t2)
                                        end of H6
                                        we proceed by induction on H6 to prove 
                                           pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                           case ex3_2_intro : x0:T x1:T H7:eq T x (THead (Bind Abst) x0 x1) H8:pr3 c u2 x0 H9:∀b0:B.∀u:T.(pr3 (CHead c (Bind b0) u) t2 x1) ⇒
                                              the thesis becomes 
                                              pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                                                 (H10) 
                                                    we proceed by induction on H7 to prove 
                                                       pr3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) x0 x1))
                                                       case refl_equal : ⇒
                                                          the thesis becomes the hypothesis H5

                                                       pr3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) x0 x1))
                                                 end of H10
                                                 (h1) 
                                                    by (drop_refl .)
                                                    we proved drop O O c c
                                                    that is equivalent to drop (r (Bind Void) O) O c c
                                                    by (drop_drop . . . . previous .)
drop (S O) O (CHead c (Bind Void) u1) c
                                                 end of h1
                                                 (h2) 
                                                    by (H9 . .)
                                                    we proved pr3 (CHead c (Bind Abst) x0) t2 x1
                                                    by (pr3_head_12 . . . H8 . . . previous)
pr3 c (THead (Bind Abst) u2 t2) (THead (Bind Abst) x0 x1)
                                                 end of h2
                                                 by (pr3_lift . . . . h1 . . h2)
                                                 we proved 
                                                    pr3
                                                      CHead c (Bind Void) u1
                                                      lift (S O) O (THead (Bind Abst) u2 t2)
                                                      lift (S O) O (THead (Bind Abst) x0 x1)
                                                 by (pc3_pr3_t . . . H10 . previous)

                                                    pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                           pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                                  pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
                      we proved 
                         pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))

                      not (eq B Void Abst)
                        →∀c:C
                             .∀t1:T
                               .∀t2:T
                                 .∀u1:T
                                   .∀u2:T
                                     .pc3 c (THead (Bind Void) u1 t1) (THead (Bind Abst) u2 t2)
                                       →pc3 (CHead c (Bind Void) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
          we proved 
             not (eq B b Abst)
               →∀c:C
                    .∀t1:T
                      .∀t2:T
                        .∀u1:T
                          .∀u2:T
                            .pc3 c (THead (Bind b) u1 t1) (THead (Bind Abst) u2 t2)
                              →pc3 (CHead c (Bind b) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))
       we proved 
          ∀b:B
            .not (eq B b Abst)
              →∀c:C
                   .∀t1:T
                     .∀t2:T
                       .∀u1:T
                         .∀u2:T
                           .pc3 c (THead (Bind b) u1 t1) (THead (Bind Abst) u2 t2)
                             →pc3 (CHead c (Bind b) u1) t1 (lift (S O) O (THead (Bind Abst) u2 t2))