proposition: Lemma functional_union : forall R1 R2, functional R1 -> functional R2 -> (forall x y z, R1 x y -> R2 x z -> False) -> functional (union R1 R2).
proof: Proof. Proof using. intros. unfold union. intros x y z Hxy Hxz. destruct Hxy; destruct Hxz; auto_false*. Qed.
imports: TLC(LibTactics LibLogic LibBool LibLogic LibProd LibSum)