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Offline Knotwilg
 Post subject: Shuei, modern endgame and AI - 2
Post #1 Posted: Sun Jun 27, 2021 4:07 pm 
Oza
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I'll post the game position first and let you discover the main theme(s) for yourself. Black to play.

Go Diagram
Position at 135
Click Here To Show Diagram Code
[go]$$B Position at 135
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . . . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X . . |
$$ | . X O . . X X . . . . . O O . . O O . |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X . . O X . X . X . . . X . . . |
$$ | . . X O X . . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Here's more information:

Go Diagram
Position at 135
Click Here To Show Diagram Code
[go]$$B Position at 135
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . b . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X . . |
$$ | . X O . . X X . . . . . O O . . O O a |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X . . O X . X . X . . . X . . . |
$$ | . . X O X . . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


1. Can the White group in the top left quadrant be attacked? If so, what's the best way to do so?
2. Can Black's centre stones be cut off?
3. There's a ko at A. Is it wise for Black to launch it? Now or later?
4. Is the "double sente" at B urgent?
5. And where would you play?

Shuei has White here. His opponent, Yasui Sanei, chose a very different move than KataGo, which the latter estimated to lose 3 points.
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Offline Knotwilg
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #2 Posted: Mon Jun 28, 2021 2:20 am 
Oza
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Let's first look at the ko. Saving the stones makes a difference of about 20 points.

Go Diagram
Ko - B7 at B1
Click Here To Show Diagram Code
[go]$$B Ko - B7 at B1
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . . . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X 9 |
$$ | . X O . O X . . X . X . O X X . X 3 2 |
$$ | . X O 6 5 X X . . . . . O O . . O O 1 |
$$ | . . X O O O X . X . . X . X . O O X 4 |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , 8 . . X X , . . . |
$$ | . O O X . . O X . X 0 X . . . X . . . |
$$ | . . X O X . . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


This is the trade: White can cut off the central Black stones.

Incidentally, this is KataGo's main line, giving Black a 5+ point lead.

This post by Knotwilg was liked by 2 people: Bill Spight, marvin
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Offline Knotwilg
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #3 Posted: Mon Jun 28, 2021 8:37 am 
Oza
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Posts: 2432
Location: Ghent, Belgium
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Rank: KGS 2d OGS 1d Fox 4d
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Online playing schedule: UTC 18:00 - 22:00
Go Diagram
The game
Click Here To Show Diagram Code
[go]$$B The game
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . 5 4 . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X . . |
$$ | . X O . . X X . . . . . O O . . O O 8 |
$$ | . . X O O O X . X 3 . X 7 X . O O X . |
$$ | . . X X . . X O 2 . . X O . O O X . X |
$$ | . X . X O O . . . . . b O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X . . O X . X . X . . . X . . . |
$$ | . . X O X a . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O 6 . |
$$ | 1 O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Yasui Sanei chose this endgame move, which I calculate as a 3 point gote. It must have added value in that it activates the potential in the center. Shuei answers with :w2: which is one of the three moves KataGo keeps switching between as the best answer, A and B being the other two.

But then Sanei answered very submissively at :b3: and the game becomes close. Shuei played the big endgame in sente and then :w6:. Sanei then picks :b7: and Shuei forestalls the ko.

In 8 moves, Sanei goes from a 5+ lead to trailing by 2+ points.

Incidentally, White can avoid the ko ...

Go Diagram
Double ko
Click Here To Show Diagram Code
[go]$$B Double ko
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . b . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O 5 |
$$ | . X O , O O X . . , . . O . O X 6 X 4 |
$$ | . X O . O X . . X . X . O X X . X 2 3 |
$$ | . X O . . X X . . . . . O O . . O O 1 |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X . . O X . X . X . . . X . . . |
$$ | . . X O X . . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

This post by Knotwilg was liked by: Bill Spight
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Offline jlt
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #4 Posted: Mon Jun 28, 2021 12:11 pm 
Gosei
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Since White can avoid the ko, why does White play the ko in Katago's main line?
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Offline Knotwilg
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #5 Posted: Tue Jun 29, 2021 9:04 am 
Oza
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Online playing schedule: UTC 18:00 - 22:00
Go Diagram
Avoiding the ko
Click Here To Show Diagram Code
[go]$$B Avoiding the ko
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . . . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X 2 . |
$$ | . X O . . X X . . . . . O O . . O O 1 |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X . . O X . X . X . . . X . . . |
$$ | . . X O X . . X . . . . O . . . . . . |
$$ | . . O O . . . . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Given sufficient playouts, blocking to avoid the ko indeed becomes the blue move, about 1,5 pts better than allowing it.

This post by Knotwilg was liked by: jlt
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Offline jlt
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #6 Posted: Tue Jun 29, 2021 10:43 am 
Gosei
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Other question: how does White live if Black blocks at G8?
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Offline Knotwilg
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #7 Posted: Tue Jun 29, 2021 12:09 pm 
Oza
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Black has too many weaknesses to really threaten a big capture.
Take this variation: Black can't handle it.

Go Diagram
Avoiding the ko
Click Here To Show Diagram Code
[go]$$B Avoiding the ko
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . . . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X . . |
$$ | . X O . . X X . . . . . O O . . O O . |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O . . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X , X . O O O , . . . X X , . . . |
$$ | . O O X 3 2 O X b X . X . . . X . . . |
$$ | . . X O X 4 1 X . . . . O . . . . . . |
$$ | . . O O 6 5 a . . . O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


%%%

Black's strongest resistance to keep the attack going is this ko. Yet a ko on such a big group is hard to win because there are so many local ko threats, starting at A. White can finish the ko by starting another one, so that this becomes heavy for Black.

Go Diagram
Avoiding the ko
Click Here To Show Diagram Code
[go]$$B Avoiding the ko
$$ ---------------------------------------
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O X X . . . . . . . . . . O . O |
$$ | . . X O O X . . X . O . . . O O X O . |
$$ | . X O , O O X . . , . . O . O X . X . |
$$ | . X O . O X . . X . X . O X X . X . . |
$$ | . X O . . X X . . . . . O O . . O O . |
$$ | . . X O O O X . X . . X . X . O O X . |
$$ | . . X X . . X O a . . X O . O O X . X |
$$ | . X . X O O . . . . . . O . O X X . . |
$$ | . O X 6 X . O O O , . . . X X , . . . |
$$ | . O O X 4 2 O X . X . X . . . X . . . |
$$ | . . X O X 3 1 X . 5 . . O . . . . . . |
$$ | . . O O . . . . . b O . . . . . . X . |
$$ | . O . . . . . . . . . . . O . X X O . |
$$ | . X O . O . . . . . . . . . . . O . . |
$$ | . O X , . O . O . , . . . O O O . . . |
$$ | . X . X X X O . . . O O O X X . O . . |
$$ | . . X . . . . . . O X X X . . X X X . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]


It's probably better for Black to keep this aji in reserve and play big endgame points instead, which is I believe the reasoning behind Sanei's move in the game. KataGo likes B as a move that takes the aji into account - but still prefers the ko/sente at the top right.

This post by Knotwilg was liked by: jlt
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Offline jlt
 Post subject: Re: Shuei, modern endgame and AI - 2
Post #8 Posted: Tue Jun 29, 2021 12:17 pm 
Gosei
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My reading indeed corresponds to your last message, I thought that indeed the ko hard to win but at least Black could gain something. For instance Black has a good ko threat at T14...

Anyway I am never able to evaluate how much a ko is worth.
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