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 Post subject: Re: Subtilities for ko threats handling
Post #21 Posted: Thu Jan 20, 2022 6:06 pm 
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Gérard TAILLE wrote:
Though I now understand the meaning of the three marked stones I did not manage to find a white move better than the marked white stone in the diagram above. Does such white move really exist?


There are 6 such moves ;-)

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 Post subject: Re: Subtilities for ko threats handling
Post #22 Posted: Fri Jan 21, 2022 4:24 am 
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dany wrote:
Gérard TAILLE wrote:
Though I now understand the meaning of the three marked stones I did not manage to find a white move better than the marked white stone in the diagram above. Does such white move really exist?


There are 6 such moves ;-)


Maybe we are in line but it seems we discuss on two different positions.
I considered only the following position resulting from Ichiriki problem, I mean with no black stone on J8.
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O W |
$$ | O O O O O X O X O O O X X |
$$ | . . . O B O O X X O O X . |
$$ | . . . O B O X . . X O O X |
$$ | . . . , B O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X . . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ +---------------------------+[/go]

In this position do you agree that the white marked is the only best move?
Do you agree also that the presence of the three marked stones is essential in order to say that the white marked stone is really the only best move?

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 Post subject: Re: Subtilities for ko threats handling
Post #23 Posted: Fri Jan 21, 2022 4:46 am 
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Gérard TAILLE wrote:
dany wrote:
Gérard TAILLE wrote:
Though I now understand the meaning of the three marked stones I did not manage to find a white move better than the marked white stone in the diagram above. Does such white move really exist?


There are 6 such moves ;-)


Maybe we are in line but it seems we discuss on two different positions.
I considered only the following position resulting from Ichiriki problem, I mean with no black stone on J8.
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O W |
$$ | O O O O O X O X O O O X X |
$$ | . . . O B O O X X O O X . |
$$ | . . . O B O X . . X O O X |
$$ | . . . , B O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X . . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ +---------------------------+[/go]

In this position do you agree that the white marked is the only best move?
Do you agree also that the presence of the three marked stones is essential in order to say that the white marked stone is really the only best move?

Yes.Yes

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 Post subject: Re: Subtilities for ko threats handling
Post #24 Posted: Fri Jan 21, 2022 4:58 am 
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The original position and my modification are the same story, the same variations. The only difference is which variation you prefer as a solution. Ichiriki prefers the eternal life variation. I prefers another variation.

original position:
Ichiriki variation - the best
another variation

modified position:
Ichiriki variation
another variation - the best

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 Post subject: Re: Subtilities for ko threats handling
Post #25 Posted: Fri Jan 21, 2022 6:28 am 
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dany wrote:
The original position and my modification are the same story, the same variations.

Did you adjust the komi while adding a Black stone to the board?

Or did you suppose that the added Black stone has captured a White one?

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The really most difficult Go problem ever: https://igohatsuyoron120.de/index.htm
Igo Hatsuyōron #120 (really solved by KataGo)

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 Post subject: Re: Subtilities for ko threats handling
Post #26 Posted: Fri Jan 21, 2022 6:35 am 
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dany wrote:
The original position and my modification are the same story, the same variations. The only difference is which variation you prefer as a solution. Ichiriki prefers the eternal life variation. I prefers another variation.

original position:
Ichiriki variation - the best
another variation

modified position:
Ichiriki variation
another variation - the best


I understand Dany and I agree with your results.
As far as I am concerned I do not like very much Eternal Life and I prefer using area scoring and superko.
Here I have to recognize that in the context of japanese rules the original position is very well built. Beside the threat handling difficulty the result is quite interesting : as soon as a player try to avoid the eternal life then this player will lose by half a point.

Ther modified position avoid the Eternal life but then the result is far less interesting because white can win in several variations.

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 Post subject: Re: Subtilities for ko threats handling
Post #27 Posted: Fri Jan 21, 2022 7:45 am 
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Gérard TAILLE wrote:
Ther modified position avoid the Eternal life but then the result is far less interesting because white can win in several variations.

No. White can win in the only variation

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 Post subject: Re: Subtilities for ko threats handling
Post #28 Posted: Fri Jan 21, 2022 8:13 am 
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In the original position, the interesting variation remains hidden behind Ichiriki solution. I do not like it. In the modified position the interesting variation becomes a solution and Ichiriki solution becomes a strong false idea))

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 Post subject: Re: Subtilities for ko threats handling
Post #29 Posted: Fri Jan 21, 2022 8:41 am 
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Cassandra wrote:
dany wrote:
The original position and my modification are the same story, the same variations.

Did you adjust the komi while adding a Black stone to the board?

Or did you suppose that the added Black stone has captured a White one?


I reduced black's score by 1 point

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 Post subject: Re: Subtilities for ko threats handling
Post #30 Posted: Fri Jan 21, 2022 9:15 am 
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dany wrote:
In the original position, the interesting variation remains hidden behind Ichiriki solution. I do not like it. In the modified position the interesting variation becomes a solution and Ichiriki solution becomes a strong false idea))


Yes Dany I agree with you but I still do not see how black has to play in order that all white moves are forced (no variation).
As an example in the following position:
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O O |
$$ | O O O O O X O X O O O . . |
$$ | . . . O X O O X X O O . O |
$$ | B . . O X O X . # X O O . |
$$ | O X X X X O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]
white can choose between several moves can't she?

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 Post subject: Re: Subtilities for ko threats handling
Post #31 Posted: Fri Jan 21, 2022 9:55 am 
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Gérard TAILLE wrote:
dany wrote:
In the original position, the interesting variation remains hidden behind Ichiriki solution. I do not like it. In the modified position the interesting variation becomes a solution and Ichiriki solution becomes a strong false idea))


Yes Dany I agree with you but I still do not see how black has to play in order that all white moves are forced (no variation).
As an example in the following position:
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O O |
$$ | O O O O O X O X O O O . . |
$$ | . . . O X O O X X O O . O |
$$ | B . . O X O X . # X O O . |
$$ | O X X X X O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]
white can choose between several moves can't she?


Yes, different moves (or different moves order). But for me it's all the same variant - black kill white's stones and white save H6

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 Post subject: Re: Subtilities for ko threats handling
Post #32 Posted: Fri Jan 21, 2022 10:39 am 
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dany wrote:
Gérard TAILLE wrote:
dany wrote:
In the original position, the interesting variation remains hidden behind Ichiriki solution. I do not like it. In the modified position the interesting variation becomes a solution and Ichiriki solution becomes a strong false idea))


Yes Dany I agree with you but I still do not see how black has to play in order that all white moves are forced (no variation).
As an example in the following position:
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O O |
$$ | O O O O O X O X O O O . . |
$$ | . . . O X O O X X O O . O |
$$ | B . . O X O X . # X O O . |
$$ | O X X X X O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]
white can choose between several moves can't she?


Yes, different moves (or different moves order). But for me it's all the same variant - black kill white's stones and white save H6

Click Here To Show Diagram Code
[go]$$
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | . . O X O . . . . -
$$ | . X X X O . . . . -
$$ | . . X O O . . . . -
$$ +-------------------+[/go]

BTW I think the area in the bottom left corner was not handled correctly for a strict local point of view (no impact for the Ichiriki problem)

Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | 2 1 O X O . . . . -
$$ | . X X X O . . . . -
$$ | . . X O O . . . . -
$$ +-------------------+[/go]

white can create another threat by
Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | X 5 . X O . . . . -
$$ | 3 X X X O . . . . -
$$ | 6 . X O O . . . . -
$$ +-------------------+[/go]

to reach the following position
Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | X O . X O . . . . -
$$ | . X X X O . . . . -
$$ | X . X O O . . . . -
$$ +-------------------+[/go]
which is a pass-alive position

Instead it seems technically strictly better for white to play
Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | 1 2 O X O . . . . -
$$ | . X X X O . . . . -
$$ | . . X O O . . . . -
$$ +-------------------+[/go]

white can still create another threat by
Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | O X . X O . . . . -
$$ | 3 X X X O . . . . -
$$ | 6 5 X O O . . . . -
$$ +-------------------+[/go]

to reach the following position
Click Here To Show Diagram Code
[go]$$W
$$ | . . . . . . . . . -
$$ | O O O O . . . . . -
$$ | X X X O . . . . . -
$$ | . X . X O . . . . -
$$ | . X X X O . . . . -
$$ | X . X O O . . . . -
$$ +-------------------+[/go]
which is NOT a pass-alive position

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 Post subject: Re: Subtilities for ko threats handling
Post #33 Posted: Fri Jan 21, 2022 11:07 am 
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dany wrote:
Gérard TAILLE wrote:
dany wrote:
In the original position, the interesting variation remains hidden behind Ichiriki solution. I do not like it. In the modified position the interesting variation becomes a solution and Ichiriki solution becomes a strong false idea))


Yes Dany I agree with you but I still do not see how black has to play in order that all white moves are forced (no variation).
As an example in the following position:
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O O |
$$ | O O O O O X O X O O O . . |
$$ | . . . O X O O X X O O . O |
$$ | B . . O X O X . # X O O . |
$$ | O X X X X O X X X , X X O |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]
white can choose between several moves can't she?


Yes, different moves (or different moves order). But for me it's all the same variant - black kill white's stones and white save H6


For the black moves it is worse:
Click Here To Show Diagram Code
[go]$$Bc
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X 1 O O |
$$ | 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 a |
$$ | . . . , X O X X X , X X . |
$$ | . . . . 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]

In original Ichiriki problem :b1: is the best move.
With the modified position it seems black can still reach the best result by beginning with "a" instead of :b1: in the diagram above.

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 Post subject: Re: Subtilities for ko threats handling
Post #34 Posted: Fri Jan 21, 2022 11:35 am 
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Gérard TAILLE wrote:

For the black moves it is worse:
Click Here To Show Diagram Code
[go]$$Bc
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X 1 O O |
$$ | 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 a |
$$ | . . . , X O X X X , X X . |
$$ | . . . . 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]

In original Ichiriki problem :b1: is the best move.
With the modified position it seems black can still reach the best result by beginning with "a" instead of :b1: in the diagram above.


I do not think so

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 Post subject: Re: Subtilities for ko threats handling
Post #35 Posted: Fri Jan 21, 2022 11:53 am 
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dany wrote:
Gérard TAILLE wrote:

For the black moves it is worse:
Click Here To Show Diagram Code
[go]$$Bc
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X 1 O O |
$$ | 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 a |
$$ | . . . , X O X X X , X X . |
$$ | . . . . 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]

In original Ichiriki problem :b1: is the best move.
With the modified position it seems black can still reach the best result by beginning with "a" instead of :b1: in the diagram above.


I do not think so


OK, let's try
Click Here To Show Diagram Code
[go]$$Bc
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X 5 O O |
$$ | O O O O O X O X O O . X 3 |
$$ | . . . O X O O X X O O 7 2 |
$$ | . . . O X O X . # X O O 1 |
$$ | . . . , X O X X X , X X 4 |
$$ | . . . . O O . O . X X O X |
$$ | O O O O . . O X X . X O 6 |
$$ | X X X O . . O O X X X O 8 |
$$ | . . O X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ +---------------------------+[/go]

Click Here To Show Diagram Code
[go]$$Bcm9
$$ +---------------------------+
$$ | . . . . . . . . X X X X . |
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O X X . . |
$$ | O O O O O X O X O O 1 X X |
$$ | . . . O X O O X X O O X O |
$$ | . . . O X O X . # X O O 3 |
$$ | . . . , X O X X X , X X O |
$$ | . . . . O O 4 O . X X O 2 |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O O |
$$ | . . O X O . . . O X O . . |
$$ | . X X X O . . . O O O O O |
$$ | . . X O O . . . . . . . . |
$$ +---------------------------+[/go]

and if I am not wrong black reaches her best result (white wins by 0.5 point).

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 Post subject: Re: Subtilities for ko threats handling
Post #36 Posted: Fri Jan 21, 2022 1:28 pm 
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W+1.5

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 Post subject: Re: Subtilities for ko threats handling
Post #37 Posted: Fri Jan 21, 2022 3:01 pm 
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dany wrote:
W+1.5

Oops sorry Dany, you are right.

Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O . |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X . |
$$ | . . d O X O X . X X O O X |
$$ | . c b a X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]

Finally, with the modified position the only weakness is when the position above is reached. From that point both players may have several choices beginning with black who can play a, b, c or d.

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 Post subject: Re: Subtilities for ko threats handling
Post #38 Posted: Fri Jan 21, 2022 4:19 pm 
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Gérard TAILLE wrote:
dany wrote:
W+1.5

Oops sorry Dany, you are right.

Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O . |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X . |
$$ | . . d O X O X . X X O O X |
$$ | . c b a X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]

Finally, with the modified position the only weakness is when the position above is reached. From that point both players may have several choices beginning with black who can play a, b, c or d.


No choices. The only road (black can play 1,3,5 in any order)
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O 4 |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X 2 |
$$ | 7 . . O X O X . X X O O X |
$$ | 6 5 3 1 X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]

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 Post subject: Re: Subtilities for ko threats handling
Post #39 Posted: Sat Jan 22, 2022 4:31 am 
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dany wrote:
Gérard TAILLE wrote:
dany wrote:
W+1.5

Oops sorry Dany, you are right.

Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O . |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X . |
$$ | . . d O X O X . X X O O X |
$$ | . c b a X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]

Finally, with the modified position the only weakness is when the position above is reached. From that point both players may have several choices beginning with black who can play a, b, c or d.


No choices. The only road (black can play 1,3,5 in any order)
Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . . X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O 4 |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X 2 |
$$ | 7 . . O X O X . X X O O X |
$$ | 6 5 3 1 X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]


Again it is right Dany

Click Here To Show Diagram Code
[go]$$c
$$ +---------------------------+
$$ | . . . . . . . a X X X X .
$$ | X X . . . . X X O O O X X |
$$ | O X X X X X O X O . . O 4 |
$$ | O O O O O X O X O O O X X |
$$ | . . . O X O O X X O O X 2 |
$$ | . . 5 O X O X . X X O O X |
$$ | . 3 . 1 X O X X X , X X W |
$$ | . . . . O O . O . X X O . |
$$ | O O O O . . O X X . X O O |
$$ | X X X O . . O O X X X O . |
$$ | X O . X O . . . O X O X X |
$$ | . X X X O . . . O O O O O |
$$ | X . X O O . . . . . . . . |
$$ +---------------------------+[/go]
The sequence above cannot be an alternative because white has a ko threat available at "a". Not that obvious is it?

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 Post subject: Re: Subtilities for ko threats handling
Post #40 Posted: Sat Jan 22, 2022 7:16 am 
Dies with sente

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Yes, "a" prevent black 5

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