proposition: Lemma gm_inner_node u : u \in gm_inner -> node u \in gm_inner.
proof: Proof. by move=> bb_u; rewrite inE -halfg_face val_gmnode ?gnodeK. 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)