proposition: Lemma inter_spec: forall x s s', In x (inter s s') <-> In x s /\ In x s'.
proof: Proof. unfold In. induction x; destruct s; destruct s'; simpl inter; rewrite ?mem_node; simpl mem; try (rewrite IHx; clear IHx); try intuition congruence. apply andb_true_iff. Qed.
imports: Bool PeanoNat BinPos OrderedType OrderedTypeEx FSetInterface