public int Compare(Producer <int> x, Producer <int> y)
        {
            Debug.Assert(x.MaxKey >= 0 && y.MaxKey >= 0); // Guarantees no overflow on next line

            return(y.MaxKey - x.MaxKey);
        }
 public int Compare(Producer <TKey> x, Producer <TKey> y)
 {
     return(_keyComparer.Compare(y.MaxKey, x.MaxKey));
 }