proposition: Lemma Prop_join_Disjoint: forall {A : Type} (P Q R : Ensemble A), Prop_join P Q R -> Disjoint A P Q.
proof: Proof. intros. destruct H. rewrite Disjoint_spec; auto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext