proposition: Lemma sub_node_clink {G : hypermap} : subrel (frel (finv node)) (@clink G).
proof: Proof. move => x y /eqP <-. by rewrite /clink/= eqxx. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph sgraph) fourcolor(hypermap geometry jordan color coloring combinatorial4ct) GraphTheory(hmap_ops)