proposition: Lemma notin_var_gen : forall E F, (forall x, x \notin E -> x \notin F) -> (var_gen E) \notin F.
proof: Proof. Proof using. intros. autos~ var_gen_spec. Qed.
imports: TLC(LibTactics LibList LibLogic LibNat LibEpsilon LibReflect)