proposition: Lemma map_snipd_ring : map snipd snipd_ring = r.
proof: Proof. by apply: map_preim => x rx; rewrite codom_snipd diskN_E inE /= rx. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan color geometry patch)