Life In 19x19

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]

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.

$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | 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 . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+

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

dany wrote:Have you heard about the real yose-and-ko monster 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.

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.

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

dany wrote:B+0.5

Fine. I agree with you.

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.

$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | 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 . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+

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.

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.

$$Bc9 White 6 at the marked point, Black 9 at 3
$$ +-------------------+
$$ | . X . 8 7 O 3 W 1 |
$$ | 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 . |
$$ | . O 5 4 O X . . . |
$$ +-------------------+

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]

Gérard TAILLE wrote:

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

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

The most difficult yose problem

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