Life In 19x19
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a rare katago l&d issue
http://lifein19x19.com/viewtopic.php?f=18&t=18302
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Author:  dhu163 [ Fri Aug 06, 2021 6:52 pm ]
Post subject:  a rare katago l&d issue

It's getting rarer to find AI bugs, but they still appear. I remember thinking around January 2021 that katago has managed to "understand" the strange seki "that Lee Changho couldn't solve", a diagram is at the end of this post: https://www.lifein19x19.com/viewtopic.p ... 89#p265889. Before then, it seemed to evaluate the group as dead, only recognising it was seki when all dame were filled, but around January, katago started to correctly evaluate it.

In a recent katago self-play game https://katagotraining.org/sgfplayer/ra ... es/547118/, just before black resigns, on move 173, black missed a chance to kill white's big group. Black should play at D11.
This implies white 172 is a blunder that should be at D11.

Even when putting it into the analysis engine of kg943, it evaluated the position as W+30-50 until I played it out until the end of the game when it swung in the opposite direction. I wouldn't have dared to post this otherwise, despite being fairly confident I'd checked all of the many variations (without AI).

I found this accidentally and manually, since I was confused as to why black resigned. It is true that in the final position white is unconditionally alive, by some tesujis that took me perhaps 1hour to figure out. It is surprisingly difficult for such a small space, but still a human level problem. Probably pro level.

Hint:
(based on G11 sente, and gaining the F13 atari whichever way black responds (white needs to play G13 or E12 first depending on B's response) Curiously, it still half works if black had pushed H8 in sente for H9 earlier. White is forced to play more precisely in that case with C12 instead of B12 and I think it is ko.


However, black playing at D11 instead of D14 gains black's potential D10 stone a critical two liberties so that moves at F11 do not force E12 even if white connects at D14 in sente (I plan for black to answer at C14 in the worst case). B's outside is also alive because B has O6 in sente.

Curiously in the semeai in the lower right, black making a slightly bigger eye at N1 seems to increase their liberties from 5 to 7 since a white placement inside the eye requires throwing in 3 stones (due to the hane), which still gives black an eye so it seems white is forced to fill the outside liberties first (at T2 and T1), however, after throwing in the 3 stones, white can throw into the eyespace again, so it would actually only be 6 liberties.

Here is a simplified diagram to demonstrate why white can't live locally.

Click Here To Show Diagram Code
[go]$$ Black to kill
$$ | X X X X X . .
$$ | O O . . X . .
$$ | . O O . X X X
$$ | . X O . . . X
$$ | . X X O O . X
$$ | O X O X X X X
$$ | O O O X . . .
$$ | . . X X . . .
$$ | . X . . . . .[/go]

Author:  lightvector [ Tue Aug 10, 2021 5:51 pm ]
Post subject:  Re: a rare katago l&d issue

Nice example! Something annoying about neural nets - if their raw judgment is wrong, the search's ability to fix them is surprisingly limited. Which is entirely *unlike* humans, who can and do adjust their judgment intra-game based on the results of their reading.

More training should fix this at some point though. Faster if I add in some starting positions from this game to be 0.0001% of training. :)

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