proposition: Lemma union_add_edge_r F G x u y: F ⊎ G ∔ [x, u, y] ≃ (F ⊎ G) ∔ [unr x, u, unr y].
proof: Proof. etransitivity. apply union_C. etransitivity. apply union_add_edge_l. etransitivity. apply (add_edge_iso (union_C _ _)). reflexivity. Defined.
imports: Coq(Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij) GraphTheory(equiv digraph setoid_bigop structures)