proposition: Lemma eq_prod4 : forall (x1 y1:A1) (x2 y2:A2) (x3 y3:A3) (x4 y4:A4), x1 = y1 -> x2 = y2 -> x3 = y3 -> x4 = y4 -> (x1, x2, x3, x4) = (y1, y2, y3, y4).
proof: Proof. Proof using. intros. subst~. Qed.
imports: TLC(LibTactics LibLogic LibReflect)