Subtilities for ko threats handling

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Gérard TAILLE
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Subtilities for ko threats handling

Post by Gérard TAILLE »

I have very rarely seen problems dealing with the handling of ko threats. Here is one I built myself:
Click Here To Show Diagram Code
[go]$$B Black to play, komi 7.5
$$ -----------------------------
$$ | X O . O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O X . |
$$ | X X O X O X X O O O O O . |
$$ | . X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X . . X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | . . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Can you manage to read this endgame? What is the best sequence? Who will win the game ?
BTW, from your experience, what is for you the level required to solve this problem by pure reading?
Why this problem? As far as I am concern I feel very weak in ko fighting.
In order to improve my level I begin to build various positions in order to try and understand how should ko threats be handled. The position above is the last one I built and I confess I was completly unable to read the endgame though all local areas seem not very complicated:
Basically I see two ko (one I the upper right corner and another in the upper left corner) and I see the following ko threats:
Click Here To Show Diagram Code
[go]$$B ko threats
$$ -----------------------------
$$ | X O . O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O X . |
$$ | X X O X O X X O O O O O . |
$$ | e X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X b . X O . c O X . |
$$ | O O O O O O O O O . O X . |
$$ | . a O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X d X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Black has three ko threats at "a" (16 points), "b" (10 points) and "c" (7 points)
White has one ko threat at "d" (14 points) and, depending of the circumstances a local ko threat at "e".

But how handling all these ko threats? When has a player to answer a ko threat instead of winning a ko?
For me it is quite difficult indeed.
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kvasir
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Re: Subtilities for ko threats handling

Post by kvasir »

Gérard TAILLE wrote:Can you manage to read this endgame? What is the best sequence? Who will win the game ?
BTW, from your experience, what is for you the level required to solve this problem by pure reading?
Not really. At least not in the right state of mind but probably could during a game. It is actually the wrong question to ask about "pure reading" because you mostly need to decide how to play it correctly and then you can figure that way out; I don't think it helps to start from the premise that it must be read out rather than deducted or just seen. If you decide black can fight to win the ko then it is not so hard to read that out but if this is inadequate you can consider alternatives. Conversely you could decide black can't or doesn't need to fight the ko and if that is inadequate try something else. Trying to brute force this without trusting your instincts is just too difficult to be practical.

I think this is the solution but too long to not put in a hide block and maybe others like to think about it before reading replies.
If black is going to win the ko fight you'd play like this as far as I can tell.
Click Here To Show Diagram Code
[go]$$B Black to play, komi 7.5
$$ -----------------------------
$$ | X O . O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O X 2 |
$$ | X X O X O X X O O O O O 1 |
$$ | . X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X 3 4 X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | . . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Click Here To Show Diagram Code
[go]$$Bcm5 Black to play, komi 7.5
$$ -----------------------------
$$ | X O 3 O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 . |
$$ | X X O X O X X O O O O O X |
$$ | 2 X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | . . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Click Here To Show Diagram Code
[go]$$Wcm8 Black to play, komi 7.5
$$ -----------------------------
$$ | X . X O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O . 1 |
$$ | X X O X O X X O O O O O X |
$$ | O X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | 3 2 O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Click Here To Show Diagram Code
[go]$$Bcm11 Black to play, komi 7.5
$$ -----------------------------
$$ | X . X O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 4 |
$$ | X X O X O X X O O O O O X |
$$ | O X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | O . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X 2 X X . X . . . . . |
$$ | O O X 3 X . X . . . . . . |
$$ -----------------------------[/go]
As it turns out black doesn't win the ko fight and we must also check if we can create a more favorable trade than losing the ko after fighting for it. Instead we assume white can win the ko fight and use smaller threats to force a trade on our terms when white ignores the ko threat. This however turns out to be about the same as fighting the ko (see next diagram). In that case we can just as well see if white plays the ko correctly before making the trade. For example make the small ko threat after white uses the second ko as a threat because that seems like something white could play incorrectly because it is necessary to use the threat of a new ko before exhausting the treats needed for the new ko.
Click Here To Show Diagram Code
[go]$$B Black to play, komi 7.5
$$ -----------------------------
$$ | X O . O O . O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O X 2 |
$$ | X X O X O X X O O O O O 1 |
$$ | . X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X . . X O . 3 O X . |
$$ | O O O O O O O O O . O X . |
$$ | . . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
Click Here To Show Diagram Code
[go]$$Wcm4 Black to play, komi 7.5
$$ -----------------------------
$$ | X O 4 O O 3 O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 O |
$$ | X X O X O X X O O O O O X |
$$ | . X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X . . X O 2 X O X . |
$$ | O O O O O O O O O . O X . |
$$ | . . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
It looks like black loses by 0.5 points.
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ez4u
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Re: Subtilities for ko threats handling

Post by ez4u »

kvasir wrote:
Gérard TAILLE wrote:Can you manage to read this endgame? What is the best sequence? Who will win the game ?
BTW, from your experience, what is for you the level required to solve this problem by pure reading?
Not really. At least not in the right state of mind but probably could during a game. It is actually the wrong question to ask about "pure reading" because you mostly need to decide how to play it correctly and then you can figure that way out; I don't think it helps to start from the premise that it must be read out rather than deducted or just seen. If you decide black can fight to win the ko then it is not so hard to read that out but if this is inadequate you can consider alternatives. Conversely you could decide black can't or doesn't need to fight the ko and if that is inadequate try something else. Trying to brute force this without trusting your instincts is just too difficult to be practical.

I think this is the solution but too long to not put in a hide block and maybe others like to think about it before reading replies.

If black is going to win the ko fight you'd play like this as far as I can tell.

...[snip - see original]

As it turns out black doesn't win the ko fight and we must also check if we can create a more favorable trade than losing the ko after fighting for it. Instead we assume white can win the ko fight and use smaller threats to force a trade on our terms when white ignores the ko threat. This however turns out to be about the same as fighting the ko (see next diagram). In that case we can just as well see if white plays the ko correctly before making the trade. For example make the small ko threat after white uses the second ko as a threat because that seems like something white could play incorrectly because it is necessary to use the threat of a new ko before exhausting the treats needed for the new ko.

...[snip - see original]

It looks like black loses by 0.5 points.
I think you are forgetting that while exhausting the ko threats in your first series of diagrams, White is forced to exchange a play inside Black's territory for a Black play at the border. This is the exchange of White 6 for Black 7 in your second diagram. This loses a point for White. It means that Black must exhaust all the ko threats in order to win. The correct result seems to be B+0.5 because of the White stone at A6 if we finish your original series of diagrams! :-)
Click Here To Show Diagram Code
[go]$$Bcm11 White connects at 11 after 15
$$ -----------------------------
$$ | X . X O O 8 O O . X X X X |
$$ | . X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 4 |
$$ | X X O X O X X O O O O O X |
$$ | O X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O 7 5 O X . |
$$ | O O O O O O O O O . O X . |
$$ | O . O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X 2 X X . X . . . . . |
$$ | O O X 3 X . X . . . . . . |
$$ -----------------------------[/go]
Dave Sigaty
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Re: Subtilities for ko threats handling

Post by John Fairbairn »

I have very rarely seen problems dealing with the handling of ko threats.
Rara avis, true, but there is one in captivity here, by Ichiriki Ryo. I don't know how you refer to other threads on L19, but you can find it by searching on "superhard" then choosing the thread "Japanese Title and League Scene."

This reference today (2022-01-17) to Ichiriki happily coincides with him winning Game 1 of the Kisei against Iyama.
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ez4u
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Re: Subtilities for ko threats handling

Post by ez4u »

But it turns out that the original White play in the upper left was not correct. White should instead capture the ko in the corner. This yields one more ko threat and seems to win the game. At the end of diagram below, White retakes the ko and both sides still have a ko threat left.
Click Here To Show Diagram Code
[go]$$Bcm5 Black 11 at 5, 13 at the marked stone
$$ -----------------------------
$$ | B O 3 O O . O O . X X X X |
$$ | 2 X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 4 |
$$ | X X O X O X X O O O O O X |
$$ | 8 X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | 6 5 O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X . X X . X . . . . . |
$$ | O O X . X . X . . . . . . |
$$ -----------------------------[/go]
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Re: Subtilities for ko threats handling

Post by ez4u »

However(!), that means that Black cannot answer the ko capture in the upper left and must connect in the upper right. Luckily, Black 13 below is big enough to win. If White answers it, she has no ko threats left. If both sides capture on the left side, Black wins. Therefore the original "subtlety" in the thread name seems to be using the second largest ko threat first and keeping the largest in reserve. If Black starts with B5 instead of E7, he will lose the game.
Click Here To Show Diagram Code
[go]$$Bcm5 Black 9 at the marked stone. White 12 at 2
$$ -----------------------------
$$ | B O . O O . O O . X X X X |
$$ | 2 X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 3 |
$$ | X X O X O X X O O O O O X |
$$ | 4 X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | . 9 O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X 6 X X . X . . . . . |
$$ | O O X 7 X . X . . . . . . |
$$ -----------------------------[/go]
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kvasir
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Re: Subtilities for ko threats handling

Post by kvasir »

ez4u wrote:I think you are forgetting that while exhausting the ko threats in your first series of diagrams,
Yes. I even remember thinking to myself something like "there is no loss making threat involved here" because that can chance how to play the ko fight.
ez4u wrote:However(!), that means that Black cannot answer the ko capture in the upper left and must connect in the upper right. Luckily, Black 13 below is big enough to win. If White answers it, she has no ko threats left. If both sides capture on the left side, Black wins. Therefore the original "subtlety" in the thread name seems to be using the second largest ko threat first and keeping the largest in reserve. If Black starts with B5 instead of E7, he will lose the game.
I did notice this. Starting the ko is slower because the new ko is approach ko but removing the liberty threatens to start a direct ko. Maybe thinking about both variations was the source of my counting mistake.
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Gérard TAILLE
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Re: Subtilities for ko threats handling

Post by Gérard TAILLE »

ez4u wrote:However(!), that means that Black cannot answer the ko capture in the upper left and must connect in the upper right. Luckily, Black 13 below is big enough to win. If White answers it, she has no ko threats left. If both sides capture on the left side, Black wins. Therefore the original "subtlety" in the thread name seems to be using the second largest ko threat first and keeping the largest in reserve. If Black starts with B5 instead of E7, he will lose the game.
Click Here To Show Diagram Code
[go]$$Bcm5 Black 9 at the marked stone. White 12 at 2
$$ -----------------------------
$$ | B O . O O . O O . X X X X |
$$ | 2 X X X X X O . O . O O X |
$$ | X O O X X X O O . O O 1 3 |
$$ | X X O X O X X O O O O O X |
$$ | 4 X O X O O X X X X X X X |
$$ | . X O X O O X X O O X X . |
$$ | X X O X X O X O . . O X . |
$$ | O O O O O O O O O . O X . |
$$ | . 9 O . . . . . . O O X . |
$$ | O O X O O O O O O O O X . |
$$ | O X X X O X X X X X X X . |
$$ | O O X 6 X X . X . . . . . |
$$ | O O X 7 X . X . . . . . . |
$$ -----------------------------[/go]
The various answers to this thread show me that such problem is really quite difficult.
This is a very good point ez4u, but I still do not think the sequence above is the correct one because the threat b13 seems to big. Are you sure that white cannot improve this sequence?
Anyway this sequence is a key point to understand the subtility I mentionned in the title.
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ez4u
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Re: Subtilities for ko threats handling

Post by ez4u »

That's it for me. I will leave any further improvements to others.
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Re: Subtilities for ko threats handling

Post by dany »

Marcel Grünauer wrote:
John Fairbairn wrote:Rara avis, true, but there is one in captivity here, by Ichiriki Ryo. I don't know how you refer to other threads on L19, but you can find it by searching on "superhard" then choosing the thread "Japanese Title and League Scene."
That would be viewtopic.php?p=259055#p259055.

(You can find the link to the post on the post's top right, where it says "#3".)
"The solution to the Ichiriki Problem A is apparently as follows - a void game."
I think white can play better and win by half a point
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Gérard TAILLE
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Re: Subtilities for ko threats handling

Post by Gérard TAILLE »

dany wrote:
Marcel Grünauer wrote:
John Fairbairn wrote:Rara avis, true, but there is one in captivity here, by Ichiriki Ryo. I don't know how you refer to other threads on L19, but you can find it by searching on "superhard" then choosing the thread "Japanese Title and League Scene."
That would be viewtopic.php?p=259055#p259055.

(You can find the link to the post on the post's top right, where it says "#3".)
"The solution to the Ichiriki Problem A is apparently as follows - a void game."
I think white can play better and win by half a point
Dany, could you give your best sequence for both ?
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Re: Subtilities for ko threats handling

Post by Gérard TAILLE »

John Fairbairn wrote:
I have very rarely seen problems dealing with the handling of ko threats.
Rara avis, true, but there is one in captivity here, by Ichiriki Ryo. I don't know how you refer to other threads on L19, but you can find it by searching on "superhard" then choosing the thread "Japanese Title and League Scene."

This reference today (2022-01-17) to Ichiriki happily coincides with him winning Game 1 of the Kisei against Iyama.
Thank you for the information John and thank you for the link Marcel.
It is quite interesting but adressed to professionnal.
I do not expect my problem being of professionnal interest ;-)
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Re: Subtilities for ko threats handling

Post by Gérard TAILLE »

Marcel Grünauer wrote:
John Fairbairn wrote:Rara avis, true, but there is one in captivity here, by Ichiriki Ryo. I don't know how you refer to other threads on L19, but you can find it by searching on "superhard" then choosing the thread "Japanese Title and League Scene."
That would be viewtopic.php?p=259055#p259055.

(You can find the link to the post on the post's top right, where it says "#3".)
Click Here To Show Diagram Code
[go]$$B Black to play
$$ -----------------------------
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X . O O |
$$ | O O O O O X O X O O . X . |
$$ | . . . O B O O X X O O . . |
$$ | . . . O B O X . . X O O . |
$$ | . . . . B O X X X . X X . |
$$ | . . . . O O . O . X X O X |
$$ | O O O O . . O X X . X O . |
$$ | X X X O . . O O X X X O . |
$$ | . . O X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ -----------------------------[/go]
Looking at the link mentionned I found this problem. My question is : what is the purpose of the three marked black stones? IOW, is the best sequence different with just the following position in which I deleted three black stones and three white stones:
Click Here To Show Diagram Code
[go]$$B Black to play
$$ -----------------------------
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X . O O |
$$ | O O O O O X O X O O . X . |
$$ | . . . . . O O X X O O . . |
$$ | . . . . . O X . . X O O . |
$$ | . . . . . O X X X . X X . |
$$ | . . . . . O . O . X X O X |
$$ | O O O O . . O X X . X O . |
$$ | X X X O . . O O X X X O . |
$$ | . . O X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ -----------------------------[/go]
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Re: Subtilities for ko threats handling

Post by dany »

dany wrote: "The solution to the Ichiriki Problem A is apparently as follows - a void game."
I think white can play better and win by half a point
uh... I was slightly wrong

white can play better and win by half a point...in another position
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X . O O |
$$ | O O O O O X O X O O . X . |
$$ | . . . O X O O X X O O . . |
$$ | . . . O X O X . # X O O . |
$$ | . . . , X O X X X , X X . |
$$ | . . . . O O . O . X X O X |
$$ | O O O O . . O X X . X O . |
$$ | X X X O . . O O X X X O . |
$$ | . . O X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ +---------------------------+[/go]
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dany
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Re: Subtilities for ko threats handling

Post by dany »

Gérard TAILLE wrote:
Click Here To Show Diagram Code
[go]$$B Black to play
$$ -----------------------------
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X . O O |
$$ | O O O O O X O X O O . X . |
$$ | . . . O B O O X X O O . . |
$$ | . . . O B O X . . X O O . |
$$ | . . . . B O X X X . X X . |
$$ | . . . . O O . O . X X O X |
$$ | O O O O . . O X X . X O . |
$$ | X X X O . . O O X X X O . |
$$ | . . O X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ -----------------------------[/go]
Looking at the link mentionned I found this problem. My question is : what is the purpose of the three marked black stones?
the purpose of these stones is to refute one of White's options

in my position modification this secondary option becomes the solution
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