proposition: Lemma edges_at_flip_edge (G : pre_graph) (e : ET) (x : VT) : edges_at (flip_edge G e) x = edges_at G x.
proof: Proof. rewrite /edges_at. apply: eq_imfset => //= e0. by rewrite !inE incident_flip. 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)