public void Case1(Sink sink, Edge edge, Trapezoid[] tList)
        {
            YNode yNode = new YNode(edge, Sink.Isink(tList[1]), Sink.Isink(tList[2]));
            XNode qNode = new XNode(edge.Q, yNode, Sink.Isink(tList[3]));
            XNode pNode = new XNode(edge.P, Sink.Isink(tList[0]), qNode);

            Replace(sink, pNode);
        }
        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);
        }