proposition: Lemma gfaceK : cancel3 gface gedge gnode.
proof: Proof. by move=> d; rewrite /= gnode_face gedge2. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(div choice order ssralg ssrnum ssrint intdiv) fourcolor(hypermap)