public void UnRegiestPen(PenBase pen)
 {
     Debug.Assert(PenCollection.Where(p => p == pen).Count() == 1);
     PenCollection.Remove(pen);
 }
 public void RegiestPen(PenBase pen)
 {
     Debug.Assert(PenCollection.Where(p => p == pen).Count() == 0);
     PenCollection.Add(pen);
 }