If , then
blocks. Then if
, then
is an atari, and then
connects.
togo: This obviously only works because there is an additional freedom at a.
The tricky move is . However,
solves the problem. Subsequently, if White a cuts the Black stones, then the atari at b transposes back to Variation 1.
The Black move at is a mistake. Now, after
, Black cannot avoid the ko at a. Even if
pushes,
can block, and then a Black move at b will be self-atari, so the ko still cannot be avoided.