proposition: Lemma sub_face_clink { G : hypermap } : @subrel G (frel face) clink.
proof: Proof. by move => u v /eqP ?; apply/clinkP; right. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries digraph sgraph) fourcolor(hypermap geometry jordan color coloring combinatorial4ct) GraphTheory(hmap_ops)