proposition: Lemma Disjoint_Union_Prop_join: forall A P Q, Disjoint A P Q -> Prop_join P Q (Union A P Q).
proof: Proof. intros. rewrite Disjoint_spec in H. split. + intros; rewrite Union_spec; tauto. + auto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext