/// <summary>
/// Adds the Edge to this PlanarGraph; only subclasses can add DirectedEdges,
/// to ensure the edges added are of the right class.
/// </summary>
/// <param name="dirEdge"></param>
protected virtual void Add(DirectedEdge dirEdge)
{
dirEdges.Add(dirEdge);
}
/// <summary>
/// Adds an outgoing DirectedEdge to this Node.
/// </summary>
/// <param name="de"></param>
public virtual void AddOutEdge(DirectedEdge de)
{
deStar.Add(de);
}