proposition: Lemma Disjoint_spec: forall A P Q, Disjoint A P Q <-> (forall x, P x -> Q x -> False).
proof: Proof. intros; split; intros. + inversion H. eapply H2. unfold In; rewrite Intersection_spec; split; eauto. + constructor. intros. unfold In; rewrite Intersection_spec. intro; apply H with x; tauto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext