proposition: Lemma cons_step_steps G G' H : steps G' H -> step G G' -> steps G H.
proof: Proof. intros E F. by setoid_rewrite F. Qed.
imports: HB(structures) Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone finite_quotient preliminaries bij equiv) GraphTheory(setoid_bigop structures pttdom mgraph mgraph2 rewriting)