DEFINITION subst1_subst1_back()
TYPE =
∀t1:T
.∀t2:T
.∀u2:T
.∀j:nat
.subst1 j u2 t1 t2
→∀u1:T.∀u:T.∀i:nat.(subst1 i u u2 u1)→(ex2 T λt:T.subst1 j u1 t1 t λt:T.subst1 (S (plus i j)) u t2 t)
BODY =
Show proof