fact: Definition oarc e x u y := e \in eset G /\ exists b, [/\ endpt G b e = x, endpt G (~~b) e = y & le G e ≡[b] u].
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)