proposition: Lemma gmgrid_edge d: (gedge d \in gmgrid) = (d \in gmgrid).
proof: Proof. by rewrite !gmgridE gedge2 orbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype path fingraph order ssralg ssrnum ssrint) fourcolor(hypermap geometry color coloring patch snip grid) fourcolor(matte)