proposition: Lemma left_Included_Union {A: Type}: forall P Q, Included P (Union A P Q).
proof: Proof. intros. intros ? ?. rewrite Union_iff. tauto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext