fact: Definition add_edge_edge (z : ecp_dart G) : ecp_dart G := match z with | IcpX => IcpXe | IcpXe => IcpX | Icp z' => Icp (edge z') end.
imports: mathcomp(all_ssreflect) GraphTheory(edone preliminaries bij) fourcolor(hypermap geometry cfmap jordan color coloring combinatorial4ct) fourcolor(walkup)