DEFINITION pr3_pr2_pr2_t()
TYPE =
       ∀c:C.∀u1:T.∀u2:T.(pr2 c u1 u2)→∀t1:T.∀t2:T.∀k:K.(pr2 (CHead c k u2) t1 t2)→(pr3 (CHead c k u1) t1 t2)
BODY =
Show proof