proposition: Lemma remove_spec : forall (s : t) (x y : elt) (Hs : Ok s), In y (remove x s) <-> In y s /\ ~X.eq y x.
proof: Proof. induction s; simpl; intros. - intuition; inv; auto. - elim_compare x a; inv; rewrite !InA_cons, ?IHs; intuition; try sort_inf_in; try order. Qed.
imports: MSetInterface OrdersFacts OrdersLists