Sunday Problem #70

Published 3 Oct 2021 by antti (last edited 11 Oct 2021)

This problem is arranged from a shape that appeared in a recent game between Oscar and Lucas Neirynck 6d. The presence of White’s t14 stone affects the corner considerably, and the correct solution is nothing short of ingenious.

Black to play.

Failure (1)
The position of white ‘a’ suggests that black 1 should be an efficient move for procuring eye shape near the side. However, this allows White to play 2–4 in the corner; after this, Black has nothing better available but to start a kō fight with 5–6.
Failure (2)
Black would therefore like to get the hane of 1 here in sente to prevent the kō above, but White can make the placement of 2. After 3–4, Black has no way to survive.
Similarly, if Black started with a move at ‘b’, white 2 would kill.
Failure (3)
The next idea, then, is to try the black diagonal of 1, preventing White’s strong attacking move there. However, White can then attack with 2, and the best Black can do is set up another kō with 3–8.
In tsumego terms, now that we have found two different kō shapes that are roughly as good, this should work as a hint that there is a better solution available.
Note that if Black plays 4 instead of 3, then white 3 kills Black unconditionally.
Failure (4)
Another way for Black to try to avoid the Failure (2) diagram is to play the descent of 1 here, and this is in fact a very strong attempt. Black 1 aims to jump to 2 next, which would succeed in forming two eyes, but White can unfortunately play at 2 himself.
Following, Black can attempt several sequences such as 3–10 here, but ultimately Black is unable to live.
Solution (1)
The 1-2 tesuji of black 1 turns out to be the best move. If White limits Black’s eye space from the right with 2, then black 3 makes a miai of 4 and 5, ensuring Black’s life.
Failure (5)
White 2 here holds a last pitfall for Black. If Black then attempts to live with 3, White has a brilliant killing combination with 4–6 – Black cannot even get a kō for life.
Solution (contd.)
However, Black can avoid this problem by directly playing 3. Now White can at best attempt the 4 placement in the corner, but then black 5 lives.

Comments (1)

antti wrote 1 week, 6 days ago:

Solution added.