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 Post subject: A common(?) semeai
Post #1 Posted: Mon Dec 11, 2023 2:22 pm 
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I have just studied the following position and I discovered ( :oops: ) my intuition was not that good. I imagine that some of you might also be wrong and that is the reason why I show you this semeai for analysis.

Click Here To Show Diagram Code
[go]$$B Black to play - What is the best black move?
$$ ------------------
$$ . . X . . . . . |
$$ . . X X X O . . |
$$ . . . . X O O . |
$$ . . . . X X O . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]

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 Post subject: Re: A common(?) semeai
Post #2 Posted: Mon Dec 11, 2023 8:29 pm 
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IGS: kvasir
I think it is like this. I recall having something similar in a game recently but I played too quickly then. Hope I'm not posting too quickly :-?

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


Click Here To Show Diagram Code
[go]$$Wm4 Direct ko for black, approach move for white.
$$ ------------------
$$ . . X . 4 3 5 . |
$$ . . X X X O 6 X |
$$ . . . . X O O 1 |
$$ . . . . X X O . |
$$ . . . . . O X O |
$$ . . . . . O X 2 |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X 7 |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]


I'm not absolutely sure if it is correct, these things are always like a series of hard tsumegos. However, this ko can go on for awhile, especially since the direct ko will be hotter and the transition move is small in comparison. Maybe black has some 22 points over white if white can fight the ko, which makes the corner around net zero.

Click Here To Show Diagram Code
[go]$$Wm4 On the other hand, if black plays this way white captures first.
$$ ------------------
$$ . . X . 4 2 3 . |
$$ . . X X X O . X |
$$ . . . . X O O 1 |
$$ . . . . X X O . |
$$ . . . . . O X O |
$$ . . . . . O X 5 |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]

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 Post subject: Re: A common(?) semeai
Post #3 Posted: Tue Dec 12, 2023 4:23 am 
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S19 is a common tesuji to reduce liberties quickly in this kind of corner shape.

That's the intuition part - which is probably wrong:) I look forward to seeing the definitive analysis in due course.

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 Post subject: Re: A common(?) semeai
Post #4 Posted: Tue Dec 12, 2023 4:58 am 
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kvasir wrote:
I think it is like this. I recall having something similar in a game recently but I played too quickly then. Hope I'm not posting too quickly :-?

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


Click Here To Show Diagram Code
[go]$$Wm4 Direct ko for black, approach move for white.
$$ ------------------
$$ . . X . 4 3 5 . |
$$ . . X X X O 6 X |
$$ . . . . X O O 1 |
$$ . . . . X X O . |
$$ . . . . . O X O |
$$ . . . . . O X 2 |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X 7 |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]


I'm not absolutely sure if it is correct, these things are always like a series of hard tsumegos. However, this ko can go on for awhile, especially since the direct ko will be hotter and the transition move is small in comparison. Maybe black has some 22 points over white if white can fight the ko, which makes the corner around net zero.


At least you confirm it is a rather common semeai!

It seems white has not find the best :w8: move in your main sequence:

Click Here To Show Diagram Code
[go]$$Wm4 Direct ko.
$$ ------------------
$$ . . X . X O 6 . |
$$ . . X X X O . X |
$$ . . . . X O O O |
$$ . . . . X X O . |
$$ . . . . . O X O |
$$ . . . . . O X X |
$$ . . . . . O X . |
$$ . . . . . O X 7 |
$$ . . . . . O X 5 |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]
That way it is a direct ko not really satisfactory for black.

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 Post subject: Re: A common(?) semeai
Post #5 Posted: Tue Dec 12, 2023 5:11 am 
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dust wrote:
S19 is a common tesuji to reduce liberties quickly in this kind of corner shape.

That's the intuition part - which is probably wrong:) I look forward to seeing the definitive analysis in due course.

The known moves for black to handle this corner are the following ones (a to e)
Click Here To Show Diagram Code
[go]$$B Black to play - What is the best black move?
$$ ------------------
$$ . . X . . a b . |
$$ . . X X X O . c |
$$ . . . . X O O . |
$$ . . . . X X O d |
$$ . . . . . O X e |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]
But which one is the best and why? OC you have to find the best black and white moves.

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 Post subject: Re: A common(?) semeai
Post #6 Posted: Tue Dec 12, 2023 8:03 am 
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Pure shape intuition. Don't know and haven't tried to read it out.

Feels like black should win this unconditionally.

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

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 Post subject: Re: A common(?) semeai
Post #7 Posted: Tue Dec 12, 2023 9:29 am 
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lightvector wrote:
Pure shape intuition. Don't know and haven't tried to read it out.

Feels like black should win this unconditionally.

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

Quite good lightvector. It is a big progress because you prove black can kill white unconditionnally. Unfortunately your moves are not all the best one to reach the best score. Some more work is still needed.

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 Post subject: Re: A common(?) semeai
Post #8 Posted: Sun Feb 11, 2024 9:31 am 
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Click Here To Show Diagram Code
[go]$$B Black to play - What is the best black move?
$$ ------------------
$$ . . X . . . . . |
$$ . . X X X O . . |
$$ . . . . X O O . |
$$ . . . . X X O . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]

After two months it's time to give you the answer to this problem.

First of all the wrong answer:
Click Here To Show Diagram Code
[go]$$B
$$ ------------------
$$ . . X . . 5 1 . |
$$ . . X X X O 9 . |
$$ . . . . X O O 7 |
$$ . . . . X X O 3 |
$$ . . . . . O X . |
$$ . . . . . O X 8 |
$$ . . . . . O X 6 |
$$ . . . . . O X 4 |
$$ . . . . . O X 2 |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]
After :b1: black territory will be only 12 points.

Click Here To Show Diagram Code
[go]$$B
$$ ------------------
$$ . . X . . . . . |
$$ . . X X X O . 1 |
$$ . . . . X O O 7 |
$$ . . . . X X O 5 |
$$ . . . . . O X 3 |
$$ . . . . . O X . |
$$ . . . . . O X 6 |
$$ . . . . . O X 4 |
$$ . . . . . O X 2 |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]
With this :b1: above the final black territory will be 13 points!

The only issue with this :b1: is to verify that black can kill the corner unconditionnaly.

Here is the proof:
Click Here To Show Diagram Code
[go]$$B :w10: at :w4:
$$ ------------------
$$ . . X 7 4 9 5 8 |
$$ . . X X X O 6 1 |
$$ . . . . X O O 2 |
$$ . . . . X X O . |
$$ . . . . . O X 3 |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . . O X . |
$$ . . . . , O O . |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]

Click Here To Show Diagram Code
[go]$$Bcm9 :b15: at :w10:
$$ ------------------
$$ . . X X 2 3 9 O |
$$ . . X X X O O . |
$$ . . . . X O O O |
$$ . . . . X X O . |
$$ . . . . . O X X |
$$ . . . . . O X . |
$$ . . . . . O X 8 |
$$ . . . . . O X 5 |
$$ . . . . . O X 4 |
$$ . . . . , O O 6 |
$$ . . . . . . O . |
$$ . . . . . . O O |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$[/go]
and white is dead

Not that easy is it?

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