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 Post subject: Superko differences
Post #1 Posted: Wed May 16, 2018 6:35 pm 
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Does anyone know of any situation whose result differs between positional superko and situational superko? Except for varying the superko flavor, any otherwise vanilla area scoring ruleset is fine. Such as New Zealand rules except with or without suicide both okay (if your example depends on it), or AGA rules.

Ideally, one that doesn't depend on any small-board pathologies (e.g. lacking any move on the entire remainder of the board that doesn't kill one's own group). Although, I'm not aware right now of even any small board examples of a difference between these two superko types, so I would already find it interesting to learn of any meaningful difference.

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 Post subject: Re: Superko differences
Post #2 Posted: Wed May 16, 2018 6:57 pm 
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Yes :



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 Post subject: Re: Superko differences
Post #3 Posted: Wed May 16, 2018 7:20 pm 
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Thanks - I was aware of sending-two-returning-one already, but I was unclear, so let me try clarify further :).

I'm looking for a starting situation with no prior history (e.g. we first reached that situation via a sequence that for all practical purposes will not have any bearing on future possible repetition), where under correct play from that situation, the resulting score differs under the two superko rules.

The example you gave is not quite a starting situation whose result differs between the two superko rules in such a way, because under both superko rules under correct play the final score is still the same. PSK only prevents a black variation that under SSK leads to still the same result for black anyways.

Maybe it can be made to work with some arrangement of the rest of the board such that with SSK and other ko threats black can actually capture the two white stones because white has no non-self-harming board plays anywhere to be able to fight back, yet with PSK black cannot profitably begin this fight in the first place? If you could do something like this and get something like SSK leading to a black-owned corner and PSK leading to a seki, that would make a quite interesting difference, although I'd still be interested if there is any situation not relying on this sort of small-board pathology.

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 Post subject: Re: Superko differences
Post #4 Posted: Thu May 17, 2018 10:43 am 
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I think some difference appear when there is a double ko elsewhere on the board, besides this seki. Then situational superko fails iirc (even without small board pathology).

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 Post subject: Re: Superko differences
Post #5 Posted: Thu May 17, 2018 3:34 pm 
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Do you have an example? It's not clear to me right now how that might work. For example in a vanilla situation where you have two players fighting over three ko mouths with nothing else unusual, unless the most recent move was a ko threat (which would change the board and lift all the ko restrictions), you either have:

* Among the 3 ko mouths, 2 favor black and 1 favors white, and it is white's turn to either play a ko threat or capture in a mouth.
* Among the 3 ko mouths, 2 favor white and 1 favors black, and it is black's turn to either play a ko threat or capture in a mouth.

Since in all the states you visit the player-to-move difference is also reflected as a positional difference (the total parity of the ko mouths) situational superko should have no difference to positional superko, right?

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 Post subject: Re: Superko differences
Post #6 Posted: Thu May 17, 2018 6:02 pm 
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Just from memory: The typical attack with sending-2 is that the attacker plays a move (threat with response) elsewhere to reset history before recapturing 1. So defender also needs a move (doesn't have to be threat) elsewhere to reset again to be safe here. Since there are more plain moves than threats usually, this doesn't work (except "small board pathology").

But with a double ko seki elsewhere, there are infinite potential threats. That still doesn't work normally, but if the attacker also plays in the double ko before starting the sending-2 attack, things get tricky. With positional superko this still doesn't work, as the attacker will be the first to have a key move restricted (not allowed to return to the same position with different player to move). But with situational superko that is allowed, and weird things start to happen.

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 Post subject: Re: Superko differences
Post #7 Posted: Fri May 18, 2018 5:35 am 
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lightvector wrote:
Does anyone know of any situation whose result differs between positional superko and situational superko?

There are some in an old thread:
viewtopic.php?f=45&t=9399
They are quite rare, I don't think there are many more known positions, but if you find a new one, please post them.:)


This post by asura was liked by: lightvector
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 Post subject: Re: Superko differences
Post #8 Posted: Fri May 18, 2018 6:03 am 
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Thanks, I think that thread mostly answers my question. There are some wacky positions there! :)

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