proposition: Lemma set_induction : forall P : t -> Type, (forall s, Empty s -> P s) -> (forall s s', P s -> forall x, ~In x s -> Add x s s' -> P s') -> forall s, P s.
proof: Proof. intros. apply (@fold_rec _ (fun s _ => P s) (fun _ _ => tt) tt s); eauto. Qed.
imports: MSetInterface PeanoNat DecidableTypeEx OrdersLists MSetFacts MSetDecide