proposition: Lemma diskN_rot : diskN (rot n0 r) =i diskN r.
proof: Proof. move=> x; apply: (etrans (has_rot _ _ _) (eq_has _ _)) => y. by apply: {x y}eq_connect => x y; rewrite /dlink /= mem_rot. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan color geometry patch)