fact: Definition del_vertex_plane_embedding := Build_plane_embedding del_vertex_emb_embedding (del_node_planar d (emb_planar g)).
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)