proposition: Lemma inter_b : mem x (inter s s') = mem x s && mem x s'.
proof: Proof. generalize (mem_iff (inter s s') x)(mem_iff s x)(mem_iff s' x)(inter_iff s s' x). destruct (mem x s); destruct (mem x s'); destruct (mem x (inter s s')); intuition. Qed.
imports: DecidableTypeEx MSetInterface