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The most difficult yose problem

https://lifein19x19.com/viewtopic.php?t=18589

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Re: The most difficult yose problem

Posted: Wed Feb 16, 2022 4:43 pm
by jmeinh
Will we ever get to see Dany's "Not yet" again?
Well, I used to hate it - a little bit, at least ;-)
But if it doesn't come again - I will certainly miss it. A little bit, at least.

Re: The most difficult yose problem

Posted: Wed Feb 16, 2022 4:48 pm
by dany
Gérard TAILLE wrote:
dany wrote: in principle, the solution too
but imho 94 white move is easier for black - black can immediately finish an unclear ko
Click Here To Show Diagram Code
[go]$$Wm94
$$ +---------------------------+
$$ | . 2 O X X X X X O . O . O |
$$ | 8 X O O O O X X O O . O O |
$$ | 6 O X X O X X X O O O O O |
$$ | 7 O X O X X , . X X X X O |
$$ | . 5 4 O O X . X X X . X X |
$$ | . O X . O X . . X . X O . |
$$ | O O O O O X O O O X X X O |
$$ | X O X X O O X X O X O X X |
$$ | X X X . X O X X X X O O O |
$$ | O . X X X O O X X X O 3 X |
$$ | O O O X X O O O X X O X 1 |
$$ | O 9 O X O O . O X O O O . |
$$ | O X O X O O . O X X O . O |
$$ +---------------------------+[/go]
B+0.5

so I prefer white's other move, which continues the ko
Click Here To Show Diagram Code
[go]$$Wm94
$$ +---------------------------+
$$ | . . O X X X X X O . O . O |
$$ | . X O O O O X X O O . O O |
$$ | . O . . O X X X O O O O O |
$$ | . O . O X X , . X X X X O |
$$ | . . 1 O O X . X X X . X X |
$$ | . O X . O X . . X . X O . |
$$ | O O O O O X O O O X X X O |
$$ | X O X X O O X X O X O X X |
$$ | X X X . X O X X X X O O O |
$$ | O . X X X O O X X X O . X |
$$ | O O O X X O O O X X O X . |
$$ | O . O X O O . O X O O O X |
$$ | O X O X O O . O X X O . O |
$$ +---------------------------+[/go]
P.S. with ko trick the solution can be extended by 4 moves
Oops as long as we talk about "preference" we have to define what is the objective.
For me I consider each player have to respect the best possible result. This best result being a black win by 0.5 point any move that will be a loss regarding this result has to be eliminated.
Click Here To Show Diagram Code
[go]$$Wm94
$$ +---------------------------+
$$ | . . O X X X X X O . O . O |
$$ | . X O O O O X X O O . O O |
$$ | . O . . O X X X O O O O O |
$$ | . O . O X X , . X X X X O |
$$ | . . 1 O O X . X X X . X X |
$$ | . O X . O X . . X . X O . |
$$ | O O O O O X O O O X X X O |
$$ | X O X X O O X X O X O X X |
$$ | X X X . X O X X X X O O O |
$$ | O a X X X O O X X X O . X |
$$ | O O O X X O O O X X O X . |
$$ | O . O X O O . O X O O O X |
$$ | O X O X O O . O X X O 2 O |
$$ +---------------------------+[/go]
Here after black :b95: white cannot play at "a" because it is great loss isn't it?
I think there are multi objectives to compare variations

black objectives (as winning side):
- max black score
- min variation length
- min complication

white objectives (as losing side):
- min black score
- max variation length
- max complication

that is, there are 3 objectives - score, length, complication

and comparison GT94 with D94 imho looks like:
score, GT94 = D94
length, GT94 > D94
complication, GT94 < D94

Re: The most difficult yose problem

Posted: Wed Feb 16, 2022 4:53 pm
by dany
Gérard TAILLE wrote: Black wins by 0.5 points after 105 moves.

the solution finally found :clap:

What move do you think was the most difficult?

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 3:53 am
by Gérard TAILLE
dany wrote:
Gérard TAILLE wrote: Black wins by 0.5 points after 105 moves.

the solution finally found :clap:

What move do you think was the most difficult?
Click Here To Show Diagram Code
[go]$$ Komi = 0.5; no prisoners
$$ +---------------------------+
$$ | . . O X X X X . O . X X . |
$$ | . . O O O . . . O . . . . |
$$ | . . . . O X X X O O O O a |
$$ | . . . O . X , . . X X X . |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X , . O X X X . |
$$ | X O X X O . X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , b O , X X X O . . |
$$ | O . . X X O O O X X O . . |
$$ | X . O 1 O . X O X O O . . |
$$ | . X O X . O . . X X O . . |
$$ +---------------------------+[/go]
The first white move was for me the most difficult white move. Seeing the big point at "a" my intuition as white is to find a sente sequence in the bottom right corner and to play at "b". It is not natural to me to find a seki gote allowing black to play at "a".
Click Here To Show Diagram Code
[go]$$Bm39 Komi = 0.5; prisoners :b6: :w2:
$$ +---------------------------+
$$ | . . O X X X X X O X X X . |
$$ | . . O O O O X O O b X X O |
$$ | . . . . O X X X O O O O O |
$$ | . . . O O X , . X X X X O |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X c . O X X X . |
$$ | X O X X O O X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , X O X X X X O . X |
$$ | O O O X X O O O X X O X . |
$$ | X X O X O . X O X O O O X |
$$ | . X O X O O a O X X O . O |
$$ +---------------------------+[/go]
For black the most difficult move for me was at the very beginning of the second phase. Seeing the two ko threats at "a" and "b" I naturally chose the move at "a" because this ko threat cost nothing while the ko threat at "b" costs 12 points. The point is that I was too lazy to calculte the exact value of the ko and the exact value of the ko threats.
When I discovered that the value of the ko was 30 points and the value of ko theats was 30 points for "b" and "only" 29 points for "a" all become clear. The ko threat at "a" can be used only after a white move move at "c" which loses 1 point.

OC it would be completly wrong to conclude I consider the other moves easy !!!

A beautiful problem which help me a lot to understand basic subtilities for handling a two-step ko.

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 4:48 am
by dany
Gérard TAILLE wrote:
dany wrote:
What move do you think was the most difficult?
Click Here To Show Diagram Code
[go]$$Bm39 Komi = 0.5; prisoners :b6: :w2:
$$ +---------------------------+
$$ | . . O X X X X X O X X X . |
$$ | . . O O O O X O O b X X O |
$$ | . . . . O X X X O O O O O |
$$ | . . . O X X , . X X X X O |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X c . O X X X . |
$$ | X O X X O O X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , X O O X X X O . X |
$$ | O O O X X O O O X X O X . |
$$ | X X O X O . X O X O O O X |
$$ | . X O X O O a O X X O . O |
$$ +---------------------------+[/go]
For black the most difficult move for me was at the very beginning of the second phase. Seeing the two ko threats at "a" and "b" I naturally chose the move at "a" because this ko threat cost nothing while the ko threat at "b" costs 12 points. The point is that I was too lazy to calculte the exact value of the ko and the exact value of the ko threats.
When I discovered that the value of the ko was 30 points and the value of ko theats was 30 points for "b" and "only" 29 points for "a" all become clear. The ko threat at "a" can be used only after a white move move at "c" which loses 1 point.

OC it would be completly wrong to conclude I consider the other moves easy !!!

A beautiful problem which help me a lot to understand basic subtilities for handling a two-step ko.
I agree. For me "b" the the most difficult move in the problem. But your explanation "The ko threat at "a" can be used only after a white move move at "c" which loses 1 point" is wrong. In the current position "a" is a valid ko threat. Beacause black has not yet added a stone in the left bottom corner. The real reason why "b" is better than "a" is described in Cassandra's diagrams.

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 5:59 am
by Gérard TAILLE
dany wrote:
Gérard TAILLE wrote:
dany wrote:
What move do you think was the most difficult?
Click Here To Show Diagram Code
[go]$$Bm39 Komi = 0.5; prisoners :b6: :w2:
$$ +---------------------------+
$$ | . . O X X X X X O X X X . |
$$ | . . O O O O X O O b X X O |
$$ | . . . . O X X X O O O O O |
$$ | . . . O X X , . X X X X O |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X c . O X X X . |
$$ | X O X X O O X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , X O O X X X O . X |
$$ | O O O X X O O O X X O X . |
$$ | X X O X O . X O X O O O X |
$$ | . X O X O O a O X X O . O |
$$ +---------------------------+[/go]
For black the most difficult move for me was at the very beginning of the second phase. Seeing the two ko threats at "a" and "b" I naturally chose the move at "a" because this ko threat cost nothing while the ko threat at "b" costs 12 points. The point is that I was too lazy to calculte the exact value of the ko and the exact value of the ko threats.
When I discovered that the value of the ko was 30 points and the value of ko theats was 30 points for "b" and "only" 29 points for "a" all become clear. The ko threat at "a" can be used only after a white move move at "c" which loses 1 point.

OC it would be completly wrong to conclude I consider the other moves easy !!!

A beautiful problem which help me a lot to understand basic subtilities for handling a two-step ko.
I agree. For me "b" the the most difficult move in the problem. But your explanation "The ko threat at "a" can be used only after a white move move at "c" which loses 1 point" is wrong. In the current position "a" is a valid ko threat. Beacause black has not yet added a stone in the left bottom corner. The real reason why "b" is better than "a" is described in Cassandra's diagrams.
You are right Dany. In fact it is difficult to answer the question "What move do you think was the most difficult" because for me the difficulty was not a specific move. The difficulty for me was to compare a ko threat at "a" with a ko threat in the upper right corner. Depending of the exact position different arguments are used and that is a great difficulty.
I showed the diagram after the 40th move where the problem began and it lasted then for several moves. Really difficult indeed.

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 6:43 am
by Gérard TAILLE
dany wrote:
Gérard TAILLE wrote: Black wins by 0.5 points after 105 moves.

the solution finally found :clap:

What move do you think was the most difficult?
Oops, it is not yet the solution. Strictly speaking white can reach 106 moves !

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 8:20 am
by jmeinh
Yes, Black captures at the top left with move 99. Although at the cost of "complexity" (but that is a matter of taste).

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 8:41 am
by Gérard TAILLE
jmeinh wrote:Yes, Black captures at the top left with move 99. Although at the cost of "complexity" (but that is a matter of taste).
I do not see to which post you answer.
It seems it is not my last one because the purpose of black is to have the shortest sequence isn't it?

Re: The most difficult yose problem

Posted: Thu Feb 17, 2022 9:09 am
by jmeinh
Gérard TAILLE wrote:
jmeinh wrote:Yes, Black captures at the top left with move 99. Although at the cost of "complexity" (but that is a matter of taste).
I do not see to which post you answer.
It seems it is not my last one because the purpose of black is to have the shortest sequence isn't it?
Well, actually it was your last one, but I had confused the objectives of W and S, so mine was nonsense :sad:

Re: The most difficult yose problem

Posted: Sun Feb 20, 2022 7:47 am
by dany
dany wrote:Several years ago, in his lecture, Alexander Dinerstein 3p talked about solving this problem.
But imho not all the important moves were explained in his lecture, and some were wrong
Alexander Dinerstein 3p: The most difficult yose problem
great explanation, even though some moves were wrong

Re: The most difficult yose problem

Posted: Sun Feb 20, 2022 10:34 am
by Gérard TAILLE
dany wrote:
dany wrote:Several years ago, in his lecture, Alexander Dinerstein 3p talked about solving this problem.
But imho not all the important moves were explained in his lecture, and some were wrong
Alexander Dinerstein 3p: The most difficult yose problem
great explanation, even though some moves were wrong
Just a question Dany. IMO the main idea of the problem is to have a difficult ko fight which have to be prepared correctly, where the ko threats are more or less hidden, and where the different ko threats have to be played in the correct order. For me the length of the sequence is not really the point.
In this sense isn't it more interesting to limit the number of ininteresting moves (filling dame while the opponent simply pass).

What about this position:
Click Here To Show Diagram Code
[go]$$c Black to play, komi 0.5
$$ +---------------------------+
$$ | . . O X X X X B O B X X . |
$$ | . . O O O W . . O . . . . |
$$ | . . . . O X X X O O O O . |
$$ | . . . O . X , . . X X X . |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X , . O X X X . |
$$ | X O X X O . X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , . O , X X X O . . |
$$ | O . . X X O O O X X O . . |
$$ | X . O . O . X O X O O . . |
$$ | . X O X . O . . X X O . . |
$$ +---------------------------+[/go]

Re: The most difficult yose problem

Posted: Mon Feb 21, 2022 10:46 am
by jmeinh
After a small change in the order of Black's ko threats (analogous to the order in the video), the White ko trick no longer seems to work, Black seems to refute it. But maybe I'm missing something...

Re: The most difficult yose problem

Posted: Mon Feb 21, 2022 11:26 am
by dany
jmeinh wrote:After a small change in the order of Black's ko threats (analogous to the order in the video), the White ko trick no longer seems to work, Black seems to refute it. But maybe I'm missing something...
Yes, if black use top right ko threats before the bottom ko threat, then the trick stops working. And it's even good. There is some artificiality and senselessness in the trick. It doesn't add anything important to the solution.

Re: The most difficult yose problem

Posted: Mon Feb 21, 2022 11:57 am
by dany
Gérard TAILLE wrote:
dany wrote:
dany wrote:Several years ago, in his lecture, Alexander Dinerstein 3p talked about solving this problem.
But imho not all the important moves were explained in his lecture, and some were wrong
Alexander Dinerstein 3p: The most difficult yose problem
great explanation, even though some moves were wrong
Just a question Dany. IMO the main idea of the problem is to have a difficult ko fight which have to be prepared correctly, where the ko threats are more or less hidden, and where the different ko threats have to be played in the correct order. For me the length of the sequence is not really the point.
In this sense isn't it more interesting to limit the number of ininteresting moves (filling dame while the opponent simply pass).

What about this position:
Click Here To Show Diagram Code
[go]$$c Black to play, komi 0.5
$$ +---------------------------+
$$ | . . O X X X X B O B X X . |
$$ | . . O O O W . . O . . . . |
$$ | . . . . O X X X O O O O . |
$$ | . . . O . X , . . X X X . |
$$ | . . . O O X . X X X . X X |
$$ | . O X . O X . . . . . O . |
$$ | O O O O O X , . O X X X . |
$$ | X O X X O . X . . X O X X |
$$ | X X X . X O X . . X O O O |
$$ | . . X , . O , X X X O . . |
$$ | O . . X X O O O X X O . . |
$$ | X . O . O . X O X O O . . |
$$ | . X O X . O . . X X O . . |
$$ +---------------------------+[/go]
with F12 and K13 stones not the same problem
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