proposition: Lemma glinkN (G : hypermap) : subrel (frel node) (@glink G).
proof: Proof. move => x y. by rewrite /glink /= => ->. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph sgraph) fourcolor(hypermap geometry jordan color coloring combinatorial4ct) GraphTheory(hmap_ops)