public override void Remove(DrawingElement element)
 {
     elements.Remove(element);
 }
 public override void Remove(DrawingElement element)
 {
     Console.WriteLine(
         "Cannot remove from a PrimitiveElement");
 }
 public override void Add(DrawingElement element)
 {
     elements.Add(element);
 }
 public override void Add(DrawingElement element)
 {
     Console.WriteLine(
         "Cannot add to a PrimitiveElement");
 }