The most difficult yose problem

[Gérard TAILLE]

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...

Let me try to change your move:

[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...

Let me try to change your move:

Well, at least I cannot refute this refutation of my "refutation". Very good! Really amazing, this ko stuff.

[dany]

Let me try to change your move:

$$Bm67
$$ +---------------------------+
$$ | . . O X X X X X O X 4 X O |
$$ | . . O O O O X X O 6 X O 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 . . . W 3 O . |
$$ | O O O O O X O 2 O X X X . |
$$ | X O X X O O X X O X O X X |
$$ | X X X . X O X 1 X X O O O |
$$ | . . X , X O O X X X O . X |
$$ | O O O X X O O O X X O X O |
$$ | . X O X O . X O X O O O 5 |
$$ | O X O X O O . O X X O 7 O |
$$ +---------------------------+

Click Here To Show Diagram Code

[go]$$Bm67
$$ +---------------------------+
$$ | . . O X X X X X O X 4 X O |
$$ | . . O O O O X X O 6 X O 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 . . . W 3 O . |
$$ | O O O O O X O 2 O X X X . |
$$ | X O X X O O X X O X O X X |
$$ | X X X . X O X 1 X X O O O |
$$ | . . X , X O O X X X O . X |
$$ | O O O X X O O O X X O X O |
$$ | . X O X O . X O X O O O 5 |
$$ | O X O X O O . O X X O 7 O |
$$ +---------------------------+[/go]

67 erase white ko threat. white fail

[Gérard TAILLE]

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...

Your proposal finally seems to works following Dany improvment.
For me the longest best sequence is now the following (102 moves):

[Gérard TAILLE]

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:

$$c Black to play, komi 0.5
$$ +---------------------------+
$$ | . . O X X X X B O B X X . |
$$ | . . 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 . . |
$$ | . X O X . O . . X X O . . |
$$ +---------------------------+

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

I do not see why the basic sequence would not be the same.

BTW what about this other position with an empty intersection at D13. Because one of the idea is to prepare the ko fight. Instead of just preparing the ko threats in the upper rignt corner this empty intersection I propose forces black to prepare in addition the ko theat in the upper left corner. That way the all variation has two more moves but it is not really the point. My view is only to add the difficulty of preparing far in advance the ko threat in the upper left corner.

$$c Black to play, komi 0.5
$$ +---------------------------+
$$ | . . O M X X X . O . X X . |
$$ | . . O O O . . . 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 . . |
$$ | . X O X . O . . X X O . . |
$$ +---------------------------+

Click Here To Show Diagram Code

[go]$$c Black to play, komi 0.5
$$ +---------------------------+
$$ | . . O M X X X . O . X X . |
$$ | . . O O O . . . 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]