proposition: Lemma ucycle_rev_cpring : ufcycle node (rev cpring).
proof: Proof. by rewrite /ucycle rev_uniq cpring_uniq cycle_rev_cpring. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)