proposition: Lemma add_vlabel_unit a x b: unit_graph a [tst x <- b] ≃ unit_graph (a⊗b).
proof: Proof. apply (unit_graph_iso (monC b a)). Defined.
imports: Coq(Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij) GraphTheory(equiv digraph setoid_bigop structures)