private Edge? GetEdgeToExtend(Graph g, Edge e) { foreach (var e2 in NonplanarSubgraph.GetAllEdges()) { if (!g.ContainsEdge(e2.U, e2.V) && g.ContainsEdge(e.V, e2.U) && g.ContainsEdge(e.V, e2.V)) { return e2; } } return null; }