In Dia. 2-11-1 four black stones are caught in a snap-back on the bottom
edge. If you have even a slight knowledge of the game, you should see
nothing strange in removing these four stones at the end without further
play. But if we think about it, this is a little strange. Black is not
in a removable state yet because he still has a liberty.
If Black plays 1 in Dia. 2-11-2 and captures White's stone, White will
recapture at 2, taking a net total of nine points of profit. If White
removes the four black stones without actually capturing them in Dia.
2-11-1 his profit is also nine points. Since the result happens to be
the same, no questions are generally raised.