proposition: Lemma edges_atE e x : e \in edges_at G x = (e \in eset G) && (incident G x e).
proof: Proof. rewrite /edges_at. by rewrite !inE. 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)