proposition: Lemma flipped_edge (G : pre_graph) e x y u : is_edge G e x u° y -> is_edge (flip_edge G e) e y u x.
proof: Proof. rewrite /is_edge /flip_edge /= !updateE. firstorder. by rewrite H2 cnvI. 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)