proposition: Lemma Complement_Included_rev: forall (U: Type) P Q, Included P Q -> Included (Complement U Q) (Complement U P).
proof: Proof. unfold Included, Complement, Ensembles.In. intros. firstorder. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext