proposition: Lemma remove_Subtract : forall x s, !!(remove x s) === Subtract _ (!!s) x.
proof: Proof. unfold Same_set, Included, mkEns, In. split; intro; set_iff; inversion 1; auto with sets. split; auto. contradict H1. inversion H1; auto. Qed.
imports: Ensembles Finite_sets MSetInterface MSetProperties OrdersEx