at
or
is shortage of liberties, and at
(or elsewhere taking a black liberty) by the same
(connect-and-die).
captures two stones, leaving equal number of liberties with Black to move...
And wins the capturing race by one move.
is a must.
Black can be even more direct - after the
stones are in a snapback.
Or if White defends the snapback, puts the white group into atari.
The atari at is wrong...
...when White plays the hane at , Black is stuck. If Black pushes at a, he is in self-atari.
Karl Knechtel, lavalyn, Scartol