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