proposition: Lemma oarc_cnv e x y u : oarc G e x u y <-> oarc G e y u° x.
proof: Proof. wlog suff W : x u y / oarc G e x u y -> oarc G e y u° x. { split; first exact: W. move/W. by rewrite cnvI. } case => E [b] [A B C]. split => //. exists (~~b). rewrite negbK. split => //. by rewrite eqvb_neq 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)