proposition: Lemma simple_rev_ring : simple (rev_ring r).
proof: Proof. by rewrite /simple froot_face_rev_ring rev_uniq rot_uniq. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry patch sew snip color chromogram) fourcolor(coloring kempe)