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Offline daniel_the_smith
 Post subject: Endgame problem from a game
Post #1 Posted: Mon Feb 21, 2011 2:20 am 
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This is a game GoCat and I just finished on OGS. It's white to play. I believe there is only one move that works.

Click Here To Show Diagram Code
[go]$$Wcm210 Position at move 209
$$ ---------------------------------------
$$ | . . . O X X . . X O O X . . . . . . . |
$$ | . . . O O X . . X O X . . . O X . . . |
$$ | . . . O X X X X X O X X X O . X O . . |
$$ | . . . O X O O . . O O X O . X X . X X |
$$ | . . . O O O X X X O X X X X O . X X O |
$$ | . . . O . O . . . O X O . X O O X O O |
$$ | . . O X . O X X X O O . . X O . O O . |
$$ | . . O X X O X . X X O O O O . O O O X |
$$ | . . O O X X X X X O O X X O O O X . X |
$$ | . . X , O X . X . O . O X X X X X X . |
$$ | . O . . . O O X . . O X . . X O X O O |
$$ | . O X . . . O X O O X X . X O O O . O |
$$ | . . X . X . O X O X O . X X X O . O O |
$$ | . X . . . . O . X X O . . X O O O O X |
$$ | . O O . . O O X X O X X X O O O X X X |
$$ | . . . , O X X X . , O . . X O X . . . |
$$ | . . . O . O X O O . X . . . X . X . . |
$$ | . . . . . O X X . . . . . . . . . . . |
$$ | . . . . . O O X . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Edit: Black has two prisoners. Everyone seems to have noticed already but I thought I should have mentioned it...

Hint:
This is the first tedomari (= get the last move) problem I've ever encountered in a real game (and recognized, anyway). I think.


I'll post my solution later. Or you can cheat and look at what I played in the game, below...


full game:


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Last edited by daniel_the_smith on Mon Feb 21, 2011 3:56 am, edited 1 time in total.
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Offline Jordus
 Post subject: Re: Endgame problem from a game
Post #2 Posted: Mon Feb 21, 2011 2:36 am 
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I would have played E13...

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Offline daniel_the_smith
 Post subject: Re: Endgame problem from a game
Post #3 Posted: Mon Feb 21, 2011 3:03 am 
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@Jordus

I was going to refute your move but I just realized it works out to the same score. So my problem is broken. :'(

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Offline HermanHiddema
 Post subject: Re: Endgame problem from a game
Post #4 Posted: Mon Feb 21, 2011 3:12 am 
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Click Here To Show Diagram Code
[go]$$Wcm210 :w20: @ a, :b21: @ b
$$ ---------------------------------------
$$ | . . . O X X . . X O O X 0 8 6 . . . . |
$$ | . . . O O X . . X O X 2 1 5 O X . . . |
$$ | . . . O X X X X X O X X X O 4 X O . . |
$$ | . . . O X O O . . O O X O 3 X X . X X |
$$ | . . . O O O X X X O X X X X O . X X O |
$$ | . . . O . O . . . O X O 9 X O O X O O |
$$ | . . O X b O X X X O O . 7 X O . O O . |
$$ | . . O X X O X . X X O O O O . O O O X |
$$ | . . O O X X X X X O O X X O O O X . X |
$$ | . . X , O X . X . O a O X X X X X X . |
$$ | . O . . . O O X . . O X . . X O X O O |
$$ | . O X . . . O X O O X X . X O O O . O |
$$ | . . X . X . O X O X O . X X X O . O O |
$$ | . X . . . . O . X X O . . X O O O O X |
$$ | . O O . . O O X X O X X X O O O X X X |
$$ | . . . , O X X X . , O . . X O X . . . |
$$ | . . . O . O X O O . X . . . X . X . . |
$$ | . . . . . O X X . . . . . . . . . . . |
$$ | . . . . . O O X . . . . . . . . . . . |
$$ ---------------------------------------[/go]


With :w10: and :w12:, white creates semedori. Since black is only one liberty ahead, he must capture these stones immediately, making :w16: and :w18: sente. Then White takes a while black takes b.

White wins by 1.5

This post by HermanHiddema was liked by 2 people: daniel_the_smith, GoCat
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Offline Jordus
 Post subject: Re: Endgame problem from a game
Post #5 Posted: Mon Feb 21, 2011 3:16 am 
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@hermenhiddema

Your solution seems to make white lose 3 or more points in the endgame with that sequence in the top...

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Offline HermanHiddema
 Post subject: Re: Endgame problem from a game
Post #6 Posted: Mon Feb 21, 2011 3:28 am 
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Jordus wrote:
@hermenhiddema

Your solution seems to make white lose 3 or more points in the endgame with that sequence in the top...


In my solution, White plays three moves in Black's territory at the top (10, 12 and 14), while black plays five moves there (11,13,15,17,19). So Black plays two more moves there than White.

If White plays elsewhere, Black captures (at O16), playing one move inside his own territory.

So the net effect of my sequence is that Black plays an extra move inside his own territory and thus White gains one point.

Try counting daniel_the_smith's variation vs my variation :)
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Offline daniel_the_smith
 Post subject: Re: Endgame problem from a game
Post #7 Posted: Mon Feb 21, 2011 3:55 am 
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Nice, Herman, didn't think of that!

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Offline Smochi
 Post subject: Re: Endgame problem from a game
Post #8 Posted: Wed Feb 23, 2011 12:49 am 
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I believe that black can throw-in at o18, both rescuing a point at the top and preventing white's making a point in the middle from becoming sente.
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Offline gaius
 Post subject: Re: Endgame problem from a game
Post #9 Posted: Wed Feb 23, 2011 3:51 am 
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@Herman:
I don't understand your :b4:. First, in your variation, white has exactly one chance to exchange :w7: / :b8: with good timing, and win another point. Right?
Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . O X X . . X O O X . . 6 . . . . |
$$ | . . . O O X . . X O X 2 1 5 O X 8 . . |
$$ | . . . O X X X X X O X X X O 4 X O . . |
$$ | . . . O X O O . . O O X O 3 X X . X X |
$$ | . . . O O O X X X O X X X X O 7 X X O |
$$ | . . . O . O . . . O X O . X O O X O O |
$$ | . . O X . O X X X O O . . X O . O O . |
$$ | . . O X X O X . X X O O O O . O O O X |
$$ | . . O O X X X X X O O X X O O O X . X |
$$ | . . X , O X . X . O . O X X X X X X . |
$$ | . O . . . O O X . . O X . . X O X O O |
$$ | . O X . . . O X O O X X . X O O O . O |
$$ | . . X . X . O X O X O . X X X O . O O |
$$ | . X . . . . O . X X O . . X O O O O X |
$$ | . O O . . O O X X O X X X O O O X X X |
$$ | . . . , O X X X . , O . . X O X . . . |
$$ | . . . O . O X O O . X . . . X . X . . |
$$ | . . . . . O X X . . . . . . . . . . . |
$$ | . . . . . O O X . . . . . . . . . . . |
$$ ---------------------------------------[/go]

If black throws in first, white does not have that chance. That is to say, it would still be sente, but because white is now in atari at every step, black can just capture white rather than connecting the corner. Also, in this variation, the semedori looks to be at least one point worse for white, and he cannot make the point at 'a' in sente.
Click Here To Show Diagram Code
[go]$$Wc :w7: @ :b4:
$$ ---------------------------------------
$$ | . . . O X X . . X O O X 8 5 . . . . . |
$$ | . . . O O X . . X O X 2 1 4 O X . . . |
$$ | . . . O X X X X X O X X X O 6 X O . . |
$$ | . . . O X O O . . O O X O 3 X X . X X |
$$ | . . . O O O X X X O X X X X O . X X O |
$$ | . . . O . O . . . O X O . X O O X O O |
$$ | . . O X . O X X X O O a . X O . O O . |
$$ | . . O X X O X . X X O O O O . O O O X |
$$ | . . O O X X X X X O O X X O O O X . X |
$$ | . . X , O X . X . O . O X X X X X X . |
$$ | . O . . . O O X . . O X . . X O X O O |
$$ | . O X . . . O X O O X X . X O O O . O |
$$ | . . X . X . O X O X O . X X X O . O O |
$$ | . X . . . . O . X X O . . X O O O O X |
$$ | . O O . . O O X X O X X X O O O X X X |
$$ | . . . , O X X X . , O . . X O X . . . |
$$ | . . . O . O X O O . X . . . X . X . . |
$$ | . . . . . O X X . . . . . . . . . . . |
$$ | . . . . . O O X . . . . . . . . . . . |
$$ ---------------------------------------[/go]


Am I mistaken?

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Offline HermanHiddema
 Post subject: Re: Endgame problem from a game
Post #10 Posted: Wed Feb 23, 2011 4:15 am 
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gaius wrote:
@Herman:
I don't understand your :b4:. First, in your variation, white has exactly one chance to exchange :w7: / :b8: with good timing, and win another point. Right?

If black throws in first, white does not have that chance. That is to say, it would still be sente, but because white is now in atari at every step, black can just capture white rather than connecting the corner. Also, in this variation, the semedori looks to be at least one point worse for white, and he cannot make the point at 'a' in sente.

Am I mistaken?


Yup, I missed the throw-in, even though it is really obvious :)
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