proposition: Lemma mergeC_eqm (G : hypermap) (x y : G) : merge x y =m merge y x.
proof: Proof. apply: EqHypermapEN => //=. exact: switchC. Qed.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij) fourcolor(hypermap geometry cfmap jordan color coloring combinatorial4ct) fourcolor(walkup)