proposition: Lemma planar_patch : planar G = planarb Gd && planarb Gr.
proof: Proof. by rewrite /planar genus_patch addn_eq0. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph) fourcolor(hypermap geometry jordan color coloring)