proposition: Lemma diskFC_face : fclosed face diskFC.
proof: Proof. move=> /= x y xFy; have:= diskF_face xFy; rewrite !inE. by rewrite (fbandF r xFy); case: (~~ _) => //= ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap jordan color geometry patch)