proposition: Lemma remove_edges_vertex (G : pre_graph) E z : (G - E) \ z ≡G G \ z - E.
proof: Proof. split => //=. by rewrite 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)