public bool Depart ()
{
int old;
int c;
CSnziState s;
do {
old = root;
Decode (old, out c, out s);
} while (Interlocked.CompareExchange (ref root, Encode (c - 1, s), old) != old);
return c != 0 && s != CSnziState.Closed;
}
#endregion