proposition: Lemma plane_emb_edge d1 d2 : adjn d1 d2 = g d1 -- g d2.
proof: Proof. exact: emb_edge. Qed.
imports: mathcomp(all_ssreflect) fourcolor(hypermap geometry color coloring walkup combinatorial4ct cfmap) GraphTheory(edone preliminaries bij digraph sgraph) GraphTheory(connectivity minor hmap_ops smerge hcycle arc)