proposition: Lemma size_cpring : size cpring = order node x0.
proof: Proof. by rewrite -(card_uniqP cpring_uniq) (eq_card mem_cpring). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry color)