proposition: Lemma diskF_rev_ring : diskF (rev_ring r) =i [predD [predC diskN r] & fband r].
proof: Proof. by move=> x; rewrite !inE diskN_rev_ring fband_rev_ring. 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)