Sunday Problem #50

Published 16 May 2021 by antti (last edited 26 May 2021)

This is a variant of the infamous carpenter’s square that comes up from time to time in games.

This is a problem for high dan amateur players, so for everybody else I have added a small spoiler that tells the end status of the problem, without actually showing any moves.

Black to play.


Black can kill unconditionally.

Failure (1)
Exchanging 1–2 turns the shape into a regular carpenter’s square. After this, black 3 will develop the corner into a kō fight in a number of ways – 4–8 is one of the most common continuations.
Failure (2)
The keima of 1 may look promising, but after white 2 there is no way to kill the corner unconditionally. Even a severe attachment such as 3 will only turn up a kō fight after 4–10.
Solution (1)
Black’s placement of 1, followed by 3 and 5, is correct move order. Following, black 7 is also an important move, aiming to start a capturing race in the corner.
Solution (2)
Up to 15, as we can see, Black barely wins the capturing race by one liberty.

Comments (1)

antti wrote 3 weeks, 6 days ago:

Solution added.