proposition: Lemma Intersection_comm: forall A P Q, Same_set (Intersection A P Q) (Intersection A Q P).
proof: Proof. intros. rewrite Same_set_spec; hnf; intros. rewrite !Intersection_spec. tauto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext