proposition: Lemma eqvG_edges_at G H : G ≡G H -> edges_at G =1 edges_at H.
proof: Proof. move => GH. move => x. apply/fsetP => e. rewrite !edges_atE -(sameE GH). case E : (_ \in _) => //=. apply: eq_existsb => b. by rewrite (same_endpt GH). 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)