proposition: Lemma oarc_eqv e x y u u' : x != y -> oarc G e x u y -> oarc G e x u' y -> u ≡ u'.
proof: Proof. move => xDy arc_e arc_e'. case: (same_oarc arc_e arc_e') xDy => -[? ? ?] //; subst. by rewrite eqxx. 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)