DEFINITION pc3_pr0_pr2_t()
TYPE =
       ∀u1:T.∀u2:T.(pr0 u2 u1)→∀c:C.∀t1:T.∀t2:T.∀k:K.(pr2 (CHead c k u2) t1 t2)→(pc3 (CHead c k u1) t1 t2)
BODY =
Show proof