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 Post subject: Re: Subtilities for ko threats handling
Post #41 Posted: Sat Jan 22, 2022 7:55 am 
Gosei

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After one week it is time for me to give you the solution:

Two ideas for this problem
1) Black will fight the ko in the upper right corner until white plays a ko threat which loses one point
2) Black must play her ko threats in the right order otherwise white will win by switching to the ko in the upper left corner



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 Post subject: Re: Subtilities for ko threats handling
Post #42 Posted: Fri Jan 28, 2022 6:45 am 
Gosei

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In this thread about ko threats handling I showed you a problem dealing with ko threat order. In the following one the idea is to deal with the value of ko threats : do I have to answer a ko threat or is it better to play an exchange? This issue is quite difficult for players who are not strong enough to count precisely the result of the game.
Here is an example:



The upper right corner is not settled and black has the opportunity either to get a seki or to fight a ko in the corner. White has a ko threat in the lower left corner but is this ko threat big enough?
The remaining part of the board is quite simple : a small yose in the center of the board.

Would you able to count correctly and find the best sequence in a real game? (as far as I am concerned I am not ;-))
What is the result of the game?


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 Post subject: Re: Subtilities for ko threats handling
Post #43 Posted: Fri Jan 28, 2022 1:58 pm 
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It's too hard for me too. In 15 minutes I can evaluate all the variations. But I almost certainly won't be able to do it in a real game

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 Post subject: Re: Subtilities for ko threats handling
Post #44 Posted: Fri Jan 28, 2022 2:59 pm 
Gosei

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dany wrote:
It's too hard for me too. In 15 minutes I can evaluate all the variations. But I almost certainly won't be able to do it in a real game


First of all I am happy to see you like such problem because I had to take a lot of time to build such position.

I often can (but not so easily ;-) ) count correctly the result of a small variation but here, with several variations and some of these being rather long, I get easily confused. At the end I am completly lost : it appears I counted some variations sevaral time and I forgot easily my previous counts.
For me such problem is an interesting challenge for players aiming at finding a rigourous approach for playing an endgame with an unclear ko remaining on the board. Sure I will make some progress by trying to be more rigourous in my approach.

Basically I have (at least) two difficulties : the visualization of all variations and the need to find the exact result for all of them.
What is for you the main difficulty? The number of variations or/and the need to count all of them?

Knowing you are 4 dan, do you think such endgame can be solved in real game by a very strong amateur?

BTW what is the result of the game according to your analyse?

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 Post subject: Re: Subtilities for ko threats handling
Post #45 Posted: Fri Jan 28, 2022 4:11 pm 
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Quote:
First of all I am happy to see you like such problem because I had to take a lot of time to build such position.

Have you heard about the real yose-and-ko monster :shock: created by Cho U?

Quote:
I often can (but not so easily ;-) ) count correctly the result of a small variation but here, with several variations and some of these being rather long, I get easily confused. At the end I am completly lost : it appears I counted some variations sevaral time and I forgot easily my previous counts.
For me such problem is an interesting challenge for players aiming at finding a rigourous approach for playing an endgame with an unclear ko remaining on the board. Sure I will make some progress by trying to be more rigourous in my approach.

Such problems are a good way to improve your reading skills. if you look at this position again and again, then over time, the calculation will become easier. My second attempt 7 min :)

Quote:
Basically I have (at least) two difficulties : the visualization of all variations and the need to find the exact result for all of them.
What is for you the main difficulty? The number of variations or/and the need to count all of them?

Visualization and sometimes calculation

Quote:
Knowing you are 4 dan, do you think such endgame can be solved in real game by a very strong amateur?

I think 6-7 dan can do it in a real game

Quote:
BTW what is the result of the game according to your analyse?

B+0.5

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 Post subject: Re: Subtilities for ko threats handling
Post #46 Posted: Sat Jan 29, 2022 5:29 am 
Oza
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It seems to me that Black can win the ko while also answering in the lower left, winning by over 10 points.

In terms of reading it out, we might first ask, "What about the seki?" Something like the first diagram will follow, but White ends up winning by 2.5, I think. This is where I would start reading and I think it is fairly straight forward. After all, if it works, we do not have to figure out the rest. Unfortunately it isn't enough.
Click Here To Show Diagram Code
[go]$$Bc9
$$ +-------------------+
$$ | . X . 1 2 O . O . |
$$ | X X X X O . O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X 5 |
$$ | O X O O O O O O X |
$$ | O X X 6 . X O O 4 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O . 3 O X . . . |
$$ +-------------------+[/go]


So Black must play the ko. The diagram below we might consider the base case. Black has a ko threat at 7, which offsets White ko threat at 4. After 9, White has no further ko threats and cannot prevent Black from capturing the top right, winning by over 10 points. I could read this out. However, see the next diagram.
Click Here To Show Diagram Code
[go]$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | X X X X O . O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X . |
$$ | O X O O O O O O X |
$$ | O X X . . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+[/go]


What if White plays 4 to eliminate Black's ko threat? Black has an interesting resource here. Connecting between 3 and 1 creates a double ko that White cannot win. White can get the rest of the yose, but still loses by over 10 points. I could not read out this double ko in my head. I only saw it using a board. So I initially assessed that White could win no matter what Black played.
Click Here To Show Diagram Code
[go]$$Bc9 Black 5 connects 3, Black 11 captures at "a"
$$ +-------------------+
$$ | . X . a 4 O 3 O 1 |
$$ | X X X X O 9 O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X 8 |
$$ | O X O O O O O O X |
$$ | O X X 0 . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 7 6 O X . . . |
$$ +-------------------+[/go]

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 Post subject: Re: Subtilities for ko threats handling
Post #47 Posted: Sat Jan 29, 2022 5:47 am 
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ez4u wrote:
It seems to me that Black can win the ko while also answering in the lower left, winning by over 10 points.

So Black must play the ko. The diagram below we might consider the base case. Black has a ko threat at 7, which offsets White ko threat at 4. After 9, White has no further ko threats and cannot prevent Black from capturing the top right, winning by over 10 points. I could read this out. However, see the next diagram.
Click Here To Show Diagram Code
[go]$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | X X X X O . O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X . |
$$ | O X O O O O O O X |
$$ | O X X . . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+[/go]



8 wrong move ;-)

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 Post subject: Re: Subtilities for ko threats handling
Post #48 Posted: Sat Jan 29, 2022 7:13 am 
Gosei

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dany wrote:
Have you heard about the real yose-and-ko monster :shock: created by Cho U?

No but surely I am interested. Do you have a link available?

dany wrote:
Such problems are a good way to improve your reading skills. if you look at this position again and again, then over time, the calculation will become easier. My second attempt 7 min :)

I agree entirely with you. By looking again and again at this position (thank you for this advice) I have greatly improved my counting process by using a quite simple rigorous method. In addition I see some progress in vizualisation though it is a little more difficult for me.

Quote:
Knowing you are 4 dan, do you think such endgame can be solved in real game by a very strong amateur?
dany wrote:
I think 6-7 dan can do it in a real game

Oops it is very high isn't it? Certainly your are right if the goal is really (that was my question indeed) to find the best sequence. If now the problem is only to find the move to play in a real game then it is different because you can easily eliminate losing moves like the seki variation or a losing ko fight.

Quote:
dany wrote:
BTW what is the result of the game according to your analyse?
dany wrote:
B+0.5

Fine. I agree with you.

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 Post subject: Re: Subtilities for ko threats handling
Post #49 Posted: Sat Jan 29, 2022 3:22 pm 
Oza
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dany wrote:
ez4u wrote:
It seems to me that Black can win the ko while also answering in the lower left, winning by over 10 points.

So Black must play the ko. The diagram below we might consider the base case. Black has a ko threat at 7, which offsets White ko threat at 4. After 9, White has no further ko threats and cannot prevent Black from capturing the top right, winning by over 10 points. I could read this out. However, see the next diagram.
Click Here To Show Diagram Code
[go]$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | X X X X O . O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X . |
$$ | O X O O O O O O X |
$$ | O X X . . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+[/go]



8 wrong move ;-)

Cool! Even with a board, I missed that. So White can capture around the outside while Black is capturing the White stones that Black ataris with 7. This is exactly the type of thing that I cannot imagine in my head. It is a step too far for my visualization capabilities.

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 Post subject: Re: Subtilities for ko threats handling
Post #50 Posted: Sat Jan 29, 2022 3:55 pm 
Gosei

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ez4u wrote:
dany wrote:
ez4u wrote:
It seems to me that Black can win the ko while also answering in the lower left, winning by over 10 points.

So Black must play the ko. The diagram below we might consider the base case. Black has a ko threat at 7, which offsets White ko threat at 4. After 9, White has no further ko threats and cannot prevent Black from capturing the top right, winning by over 10 points. I could read this out. However, see the next diagram.
Click Here To Show Diagram Code
[go]$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | X X X X O . O X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X . |
$$ | O X O O O O O O X |
$$ | O X X . . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+[/go]



8 wrong move ;-)

Cool! Even with a board, I missed that. So White can capture around the outside while Black is capturing the White stones that Black ataris with 7. This is exactly the type of thing that I cannot imagine in my head. It is a step too far for my visualization capabilities.


Yes Ez4u I was very satisfied to discover this hidden exchange. In addition you will find that the remaining sequence is still not obvious due to the special configuration of the small yose in the middle of the board. You have to recognize that all black moves are unique against the best white defense.

BTW white can force a longer defense by beginning with:
Click Here To Show Diagram Code
[go]$$B White 8 at the marked point
$$ +-------------------+
$$ | . X . . . O 3 O 1 |
$$ | X X X X O 5 W X X |
$$ | . X X O O O X . X |
$$ | X X O X X X X X 4 |
$$ | O X O O O O O O X |
$$ | O X X . . X O O 2 |
$$ | O O X X O O O . O |
$$ | . O X X O X . O . |
$$ | . O 7 6 O X . . . |
$$ +-------------------+[/go]

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 Post subject: Re: Subtilities for ko threats handling
Post #51 Posted: Sun Jan 30, 2022 1:07 pm 
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Gérard TAILLE wrote:
dany wrote:
Have you heard about the real yose-and-ko monster :shock: created by Cho U?

No but surely I am interested. Do you have a link available?

The most difficult yose problem

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 Post subject: Re: Subtilities for ko threats handling
Post #52 Posted: Mon Feb 07, 2022 9:01 am 
Gosei

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Solution of the problem; congratulation for those who managed to solve it.
Against the best white defense all black moves are unique to win.



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