proposition: Lemma add_vlabel_C F x a y b: F [tst x <- a] [tst y <- b] ≃ F [tst y <- b] [tst x <- a].
proof: Proof. Iso bij_id bij_id xpred0. split=>//=. move=>v. case eq_op; case eq_op=>//. by rewrite 2!monA (monC a b). Defined.
imports: Coq(Morphisms RelationClasses) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij) GraphTheory(equiv digraph setoid_bigop structures)