proposition: Lemma add_vlabel2_C F x a y b: F [tst x <- a] [tst y <- b] ≃2 F [tst y <- b] [tst x <- a].
proof: Proof. Iso2 (add_vlabel_C _ _). Defined.
imports: HB(structures) Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij equiv) GraphTheory(setoid_bigop structures pttdom mgraph ptt)