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 Post subject: Positions where PSK and SSK yield different results?
Post #1 Posted: Wed Nov 20, 2013 3:58 pm 
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I've always had a preference for positional superko over situational superko because it requires a bit less memorization, and since using one or the other doesn't seem to make any difference in practice, the easier rule should be preferable. However, is this really so? Does anyone know of any position where positional and situational superko yield different results?

According to Robert Jasiek, "[t]he actual difference of positional super ko and situational super ko as to occuring positions is rather small. Very few distinguishing examples are known."

Intuitively, one would be tempted to say that there are no such positions because, if the position after a player's board play is the same as a previous position where it was the player's turn instead, then that play would seem equivalent to passing. But, of course, it's not completely equivalent, since running through the cycle will cause the positions in it to be added to The List...

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #2 Posted: Wed Nov 20, 2013 4:25 pm 
Oza

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I am not a fan of the superko idea as it seems too contrived. But that is another issue and I don't want to hijack the thread by starting that discussion.

The reason I bring it up is that it seems against the spirit of the Oriental origins of the game as I understand them and I was wondering if any of the Asian countries use it regularly in their professional games.

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #3 Posted: Wed Nov 20, 2013 4:35 pm 
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A very simple case is "sending two returning one" - here PSK vs SSK doesn't matter for the result but only for the game tree.

A real difference for the result is "sending three returning two".
http://senseis.xmp.net/?SendingThreeReturningTwo

These positions seem to be really rare, I wonder how many types exists and how many are already known...

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #4 Posted: Wed Nov 20, 2013 4:59 pm 
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To sleepy to check now, but PSK/SSK look at sending-2-returning-1 starting from an unstable state. NSK/SSK could have been moonshine-life.

Oh, and molasses ko, of course.

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #5 Posted: Wed Nov 20, 2013 5:22 pm 
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DrStraw wrote:
The reason I bring it up is that it seems against the spirit of the Oriental origins of the game as I understand them and I was wondering if any of the Asian countries use it regularly in their professional games.


Technically China has it in the rules but it seems in practice they defer to no result.


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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #6 Posted: Wed Nov 20, 2013 6:54 pm 
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I guess I should clarify that I'm always referring to Chinese-style rules (area-scoring, no suicide). This said:

asura wrote:
A real difference for the result is "sending three returning two".
http://senseis.xmp.net/?SendingThreeReturningTwo

RobertJasiek wrote:
Oh, and molasses ko, of course.

Please correct me if I'm wrong, but I can't see how PSK and SSK yield different results in those cases:





Am I missing something?

RobertJasiek wrote:
PSK/SSK look at sending-2-returning-1 starting from an unstable state. NSK/SSK could have been moonshine-life.

Could you clarify this? I don't know what you mean. I thought the result of sending-2-returning-1 was the same under PSK, SSK and NSK.


Attachments:
Molasses ko.sgf [741 Bytes]
Downloaded 532 times
Sending three, returning two.sgf [548 Bytes]
Downloaded 525 times

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #7 Posted: Thu Nov 21, 2013 12:37 am 
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Molasses ko: PSK: fight for last tenuki, SSK: coexistence.

Sending-2: start from one of these positions:

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


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


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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #8 Posted: Thu Nov 21, 2013 1:50 am 
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luigi wrote:
...
Please correct me if I'm wrong, but I can't see how PSK and SSK yield different results in those cases:





Am I missing something?
...

Sorry for what may be a really stupid question (I don't know much about superko and am too old and lazy to learn), but why aren't the White passes (White 6 in the first example and White 10 in the second example) illegal under SSK? They recreate a preexisting position with the same person to play.

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #9 Posted: Thu Nov 21, 2013 2:31 am 
Tengen

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PSK/SSK/NSK are meant to restrict plays, but not passes.

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #10 Posted: Thu Nov 21, 2013 7:22 am 
Dies with sente

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Luigi, in the "sending 3 returning 2" example after white passes with 5,
then black could/should also pass with 6 (instead of playing in the corner).
Now the game is over and black is alive.

edit: It depends a bit on the used rule if the game is really over (and thus black lives) after white and black passes with 5 and 6. For example with a three pass rule to end the game it wouldn't work.


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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #11 Posted: Thu Nov 21, 2013 8:36 am 
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asura wrote:
Luigi, in the "sending 3 returning 2" example after white passes with 5,
then black could/should also pass with 6 (instead of playing in the corner).
Now the game is over and black is alive.

Ah, of course. Thanks.

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #12 Posted: Wed Nov 01, 2017 4:31 am 
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RobertJasiek wrote:
Molasses ko: PSK: fight for last tenuki, SSK: coexistence.

I see. Under PSK, at the game's end, whoever passes first loses the molasses ko, and so a pass fight ensues.

RobertJasiek wrote:
Sending-2: start from one of these positions:

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


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

I think this might be wrong, though. If White takes the corner point at the first opportunity, Black dies regardless of the superko rule used, right?

For the first diagram, I'm thinking something like this:

Click Here To Show Diagram Code
[go]$$B :b3: passes, :w4: at :b1:. Black dies
$$ +---------------------------------------+
$$ | 1 O . X O . . . . . . . . . . . . . . |
$$ | 2 X X X O . . . . . . . . . . . . . . |
$$ | . X O O O . . . . . . . . . . . . . . |
$$ | X X O , . . . . . , . . . . . , . . . |
$$ | O O O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

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 Post subject: Re: Positions where PSK and SSK yield different results?
Post #13 Posted: Wed Nov 01, 2017 9:15 am 
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Hi,
here is a example where PSK and SSK lead to a different result if you foolishly start the cycle.



Attachments:
Seki.sgf [719 Bytes]
Downloaded 175 times

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