proposition: Lemma Union_Empty_right {A: Type}: forall P, Same_set (Union _ P (Empty_set A)) P.
proof: Proof. intros. rewrite Same_set_spec. hnf; intros. rewrite Union_spec. pose proof Noone_in_empty A a. tauto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext