proposition: Lemma dscore_cface x y : cface x y -> dscore x = dscore y.
proof: Proof. by move=> xFy; rewrite /dscore (arity_cface xFy) (eq_bigl _ _ (same_cface xFy)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) mathcomp(bigop order ssralg ssrnum ssrint) fourcolor(hypermap geometry part)