proposition: Lemma simple_catCA p1 p2 p3 : simple (p1 ++ p2 ++ p3) = simple (p2 ++ p1 ++ p3).
proof: Proof. by rewrite /simple !map_cat uniq_catCA. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan)