Sunday Problem #56
Published 27 Jun 2021 by
(last edited 5 Jul 2021)
This is a tricky problem that featured in the recent Go JAM. I cannot quite remember the origin of this problem; I vaguely recall seeing this in one of Go Seigen’s tsumego collections, but could not quickly find it again.
Black to play.
First idea The attachment of 1 is probably the first move that comes to mind, but after 2–4 there is no way for Black to reduce White to one eye.
No better If white 2 in the previous diagram is a key point, then it makes sense for Black to claim it first. However, again, after 2–4, there is no way for Black to reduce White to one eye, even with a kō.
Failure If white 2 in the previous diagram is also a key point, then Black might consider trying it, too; but, after white 2 there is nothing more Black can try to attack White.
Solution The unlikely move of black 1 is correct. White should block with 2, and then after 3–7 the corner ends in a one-move approach kō in White’s favour. This is the best Black can do. If White plays at 3 instead of 2, then Black 5 kills White unconditionally.
White resists White might try to resist the kō with 4, 6, 8, and 10 in this diagram. However . . .
White resists (2) . . . after 11–13 in this diagram, White notices that there is no way for him to catch the two black stones inside his prospective second eye. This white group ends up captured.