proposition: Lemma gm_inner_closed : fclosed node gm_inner.
proof: Proof. by apply/(intro_closed cnodeC)=> u _ /eqP<-; apply: gm_inner_node. 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)