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);
}