proposition: Lemma gmdart_plain : plain gmdart_map.
proof: Proof. apply/plainP=> /= u _; rewrite gmedge2 -val_eqE /=. by rewrite (contraFneq _ (neq_halfg_edge u)) => // ->. 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)