proposition: Lemma gtouch_l p : subpred (ltouch p) (gtouch p).
proof: Proof. by case: p => x y; apply/subgrectE; rewrite !ler_add2l. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)