proposition: Lemma edges_atF b e x (edge_e : e \in eset G) : e \notin edges_at G x -> (endpt G b e == x = false).
proof: Proof. rewrite !inE /= edge_e /=. apply: contraNF => ?. by existsb b. 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)