Life In 19x19

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[go]$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . W , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

This position is from a game I played on Fox against another 3d. I was Black and played K16. KataGo's second favorite move is the similar move L17 but its top choice is something I did not expect at all. Can you guess it?

Things I might consider:
- Random move in the center, let's say J9. This is probably not unexpected enough to be the answer, and also it would be very hard to guess the exact correct spot.
- Peeping at D9. if white just connects I can't see how it can be a bad exchange. Maybe white can try to punish by blocking B10, forcing black to slide into the corner and getting sente.
- Just sliding to B17 and not give a damn about the outside. But if you think this is good enough, you might as well peep D9 first since the only way for white to "punish" was to force black to slide.
Cut D11. Looks very overplayish but what do I know. It doesn't look like black can get captured and around such white strength maybe just fighting and living somehow is good enough for black. I've definitely seen KataGo play crazier looking cuts.

So I guess the answer is most likely D9 or D11. D11 is definitely more unexpected, but I'll answer D9 since it's so much more likely to be actually good.

jussius got it!

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[go]$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . 3 . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . O , . . . . . , . . . . . , . . . |
$$ | . . 2 1 . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

In retrospect I can be convinced that this is a good exchange, but wow, that is not a move that would ever be on my candidate list. (KataGo thinks the game is pretty even, by the way.)

In retrospect I can be convinced that this is a good exchange, but wow, that is not a move that would ever be on my candidate list.

But haven't you thought the same sort of thing about many human pro moves? And in those cases, didn't you get a human explanation?

John Fairbairn wrote: But haven't you thought the same sort of thing about many human pro moves?

Yes.

And in those cases, didn't you get a human explanation?

Sometimes.

It's still not clear to me why D9 is sente.

Click Here To Show Diagram Code

[go]$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . 7 . O . . . . . . . . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . 2 . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | 6 X O . . . . . . . . . . . . . . . . |
$$ | . 4 W , . . . . . , . . . . . , . . . |
$$ | . 5 3 1 . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

White's thickness is broken.

D11 doesn't really work, because after atari, it is nearly in a net. At least certainly not without making a crude exchange of D15 for E15.

D9 is clever.
Tenuki for the B groups is fine as B16 can be met by B15 after which W has some cutting points at C16 which become exposed if W wants to force with B10, so it likely becomes gote. In the worst case, B can add a move at A14 without losing too much. And the lower left B group is safely alive, so B10 isn't particularly big either to threaten it.

However if B eventually must connect at A10, then W has B9, B8 in sente, which happen as soon as W plays B16 pretty much. Given that, W B16 is the best local move, much bigger than B10, we expect it for evaluation. In that case D9 for C9 is an excellent exchange.

W does owe a move to defend the cuts as it is in the middle of W's big potential (with potential to destroy both above and below), it concerns B's C15 group, as well as the D15 cut and D5 also. With K4, the lower left W wall isn't alive and doesn't even have room to make much of a base.

Finally, if W tries to resist with B10, then B is content to play the big move at B17 to live. W B2 remains not sente because B can crawl B8 in sente. Most importantly, later, B can play something like E5 with more power because there are more undefended cuts at C9 and D11. Even just jumping out around G9 may become interesting. Or sometimes even D5 directly (though locally net now).

__

As far as I can tell, the main question mark is if W can play B16 (fighting spirit). If B can only block B15, it seems like a good exchange, though W could get that anyway. However, if B can play C9, then perhaps W B16 simply doesn't work. It looks tricky though.

In this case fighting spirit means not getting forced into bad shape when you have a weak point (C9) that might be defendable by leaning on your opponent's weak point (the group not 100% alive), perhaps before taking gote to defend. It can go wrong if your weak point is bigger or faster (less moves to activate) than your opponent's. This judgement is tricky.

This is another alternative variation I am thinking about. Evaluation isn't easy.

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[go]$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . O O X O . . . . . . . . . . . . . . |
$$ | . O X O . . . . . . . . X . . . . . . |
$$ | . O X , O . . . . , . . . . . X . . . |
$$ | . X X . . . . . . . . . . . . . . . . |
$$ | O . X O . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O , . . . . . , . . . . . , . . . |
$$ | . X O X . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

dfan wrote:jussius got it!

$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . 3 . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . O , . . . . . , . . . . . , . . . |
$$ | . . 2 1 . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+

Click Here To Show Diagram Code

[go]$$c Black to play
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . 3 . . . . . . . . |
$$ | . . . , O . . . . , . . . . . X . . . |
$$ | . . X . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . X O O . . . . . . . . . . . . . . . |
$$ | . X X O . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . O , . . . . . , . . . . . , . . . |
$$ | . . 2 1 . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . X O . . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . X . . . . . X . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

In retrospect I can be convinced that this is a good exchange, but wow, that is not a move that would ever be on my candidate list. (KataGo thinks the game is pretty even, by the way.)

Why do you think it's a good exchange? White's stones seem more solid to me, now.

I mean, I get it. The AI said it's the right move. But why?

FWIW, I haven't played go for a few weeks, so my intuition may be off.

Well, you're stronger than me, so I shouldn't be telling you anything! Also I was careful to say "I could be convinced that this is a good exchange", not "I think this is a good exchange".

But anyway, the reason I could be convinced is that it seems faintly possible that could become useful at some point (helping with a cut or erasure), while doesn't seem to do anything for White; White was already super strong and I didn't think it helps against either Black group.

dhu163 had some more concrete analysis later on this thread.

Kirby wrote:Why do you think it's a good exchange? White's stones seem more solid to me, now.

I mean, I get it. The AI said it's the right move. But why?

Nicely highlighting John's comments from a while back about a human pro being able to explain rather than just giving an answer.

More seriously, to me this looks similar to a standard peep against a tiger's mouth shape--it's good technique that doesn't lose anything for Black and puts a stone down in a place that might be useful in one game out of a hundred. The other 99 games it doesn't matter one way or the other.