After , White can catch Black in a net with
.
and
can be exchanged without changing the result.
Black should have played at .
Brent: Then what? How does Black continue after ?
at
.
Because will force a protective move, anyway. Even if Black can play
-
with sente, Black will have to play
.
OTOH, if Black plays at a, he threatens , saving
.
It is a very close call. Depending on the rest of the board, could be better.
See One-Two-Three.
Gronk: I was surprised not to see discussion of the possibility of ko.
Gronk: Therefore, at
is safer.