proposition: Lemma relabel_add_edge F x y u: relabel (F ∔ [x, u, y]) ≃ relabel F ∔ [x, fe u, y].
proof: Proof. Iso bij_id bij_id xpred0. by split=>//; case. Defined.
imports: HB(structures) Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij equiv) GraphTheory(setoid_bigop structures pttdom mgraph ptt)