proposition: Lemma remove_vertex_edges G E z : G \ z - E ≡G (G - E)\z.
proof: Proof. split => //. by rewrite /remove_vertex/= edges_at_remove_edges fsetDDD fsetDDl fsetUC. Qed.
imports: HB(structures) Coq(Relation_Definitions Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij equiv) GraphTheory(setoid_bigop structures pttdom rewriting) GraphTheory(finmap_plus)