private static int IndexOfBoundary(List <PointSet> T, Boundary C)
 {
     for (int index = 0; index < T.Count; index++)
     {
         Boundary elem = T[index] as Boundary;
         if (elem != null && C.Equals(elem))
         {
             return(index);
         }
     }
     throw new Exception("Border not found!");
 }