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Mildly interesting tesuji from KataGo
http://www.lifein19x19.com/viewtopic.php?f=15&t=17720		 Page 1 of 1
Author:  le_4TC [ Wed Aug 12, 2020 5:42 am ]
Post subject:  Mildly interesting tesuji from KataGo
This is a common 9x9 opening:
Click Here To Show Diagram Code
[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . 9 . , . . |
$$ | . . 5 7 8 1 . . . |
$$ | . . 4 3 6 . . . . |
$$ | . . . 2 0 . . . . |
$$ | . . , . . . , . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]


KataGo thinks the game is completely even (assuming 7.0 komi), and may continue like this:
Click Here To Show Diagram Code
[go]$$Bm11
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X 1 , . . |
$$ | . . X X O X . . . |
$$ | . 5 O X O . . 7 . |
$$ | . . 3 O O . 2 8 . |
$$ | . 6 4 . . . , . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]


At this point KataGo finds a tesuji for black which seems to be the only move to keep the game a draw (every other move loses as far as I can tell). I wouldn't have found it in a real game, but I think with the hint that there is a tesuji it shouldn't be too hard to guess!

Click Here To Show Diagram Code
[go]$$Bm19 Black to play and draw (7 komi, area scoring)
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X X , . . |
$$ | . . X X O X . . . |
$$ | . X . X O . . X . |
$$ | . . X O O . O O . |
$$ | . O O . . . , . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]
Author:  le_4TC [ Thu Aug 13, 2020 10:50 am ]
Post subject:  Re: Mildly interesting tesuji from KataGo
Solution:

Click Here To Show Diagram Code
[go]$$B Wedge!
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X X , . . |
$$ | . . X X O X . . . |
$$ | . X . X O . . X . |
$$ | . . X O O 1 O O . |
$$ | . O O . . . , . . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]


White can capture the wedging stone, but that's a losing mistake. Here's one of the variations:
Click Here To Show Diagram Code
[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X X , . . |
$$ | . . X X O X . . . |
$$ | . X . X O 2 3 X 8 |
$$ | . 7 X O O 1 O O . |
$$ | . O O 5 6 a 4 . . |
$$ | . . . 9 0 . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]


(If W4 at "a" instead, black gets the sente hane-connect on the first line.)

Click Here To Show Diagram Code
[go]$$Bm11 B+2
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . 9 7 |
$$ | . . , . X X , 5 6 |
$$ | . . X X O X . b 8 |
$$ | . X . X O O X X O |
$$ | . X X O O X O O . |
$$ | 3 O O X O . O . . |
$$ | . 1 2 X O . . . . |
$$ | . . . 4 . . . . . |
$$ +-------------------+[/go]

If B15 were played at "b" instead, white would play out the local sente sequence and then win the ko in the lower left, getting a draw. For the same reason, black shouldn't atari before connecting with 19, leaving that ko threat is important. When black backs off with 15 and connects with 19, white has no opportunity to start and win the lower left ko, and the result will be B+2.

Better for white is to play atari from below after the initial wedge. There are multiple variations leading to a draw, here's one of them:
Click Here To Show Diagram Code
[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X X , . . |
$$ | . . X X O X . 6 . |
$$ | . X . X O 3 . X . |
$$ | 9 5 X O O 1 O O . |
$$ | 7 O O . . 2 4 . . |
$$ | 8 . . . . . . . . |
$$ | . 0 . . . . . . . |
$$ +-------------------+[/go]


Click Here To Show Diagram Code
[go]$$Bm11 Draw.
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . 9 7 |
$$ | . . , . X X , 3 4 |
$$ | . . X X O X 5 O 6 |
$$ | . X . X O X 1 X 2 |
$$ | X X X O O X O O 8 |
$$ | X O O . . O O . . |
$$ | O . . . . . . . . |
$$ | . O . . . . . . . |
$$ +-------------------+[/go]


If white connects on the other side with 4, this clamp is winning for black:
Click Here To Show Diagram Code
[go]$$B
$$ +-------------------+
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ | . . , . X X , . . |
$$ | . . X X O X . . . |
$$ | . X . X O 3 . X . |
$$ | . . X O O 1 O O . |
$$ | . O O . 4 2 , 5 . |
$$ | . . . . . . . . . |
$$ | . . . . . . . . . |
$$ +-------------------+[/go]


Hopefully I didn't make any mistakes in my interpretation of KataGo's analysis, let me know if something seems wrong!
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