public void Case3(Sink sink, Edge edge, Trapezoid[] tList)
        {
            YNode yNode = new YNode(edge, Sink.Isink(tList[0]), Sink.Isink(tList[1]));

            Replace(sink, yNode);
        }
 private Trapezoid Locate(Edge edge)
 {
     return(_head.Locate(edge).Trapezoid);
 }