JoelR: ... and a picks up.
limits White's eyespace, and forces
.
threatens to cut at
. If
at a, then
at
, and Black has more liberties.
Dieter: If here,
starts an approach ko (
at a), which is favorable for Black.
If here instead,
makes it a seki.
would be a mistake. Black throws in and wins the capturing race by one liberty.
If Black wants to avoid the approach ko, he could make the placement of but
is as vital a point:
White lives with seki. She can also play at
, if a direct ko is what she wants.
... but in my opinion, this is the solution. It's almost the same as the earlier approach ko solution, but Black can have White play one more ko-threat. In other words, will count as a ko-threat.
The order of play can be reversed.
Bill: Well, it can be reversed, but . . . .
If and
,
is essential.
In this variation, a and b are miai to kill.
Bill: I think this is the right third move.
There are several variations.