proposition: Lemma Prop_join_x1: forall {U} (A: Ensemble U) (a: U), ~ A a -> Prop_join A (eq a) (fun x => A x \/ x = a).
proof: Proof. intros. split; intros. + assert (a = a0 <-> a0 = a) by (split; intros; congruence). tauto. + subst; auto. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Equivalence Coq.Sets.Ensembles Coq.Sets.Constructive_sets CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext