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natural situational superko [#1654]

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willemien: natural situational superko (2008-12-08 17:06) [#5391]

I would like to make a page about it but honestly I don't understand what it is and how it differs from an situational super ko. So therefore this question. (to persuade somebody more knowledgable than me to make this page) from [ext] http://home.snafu.de/jasiek/superko.html

natural situational super ko: A player may not use a board play to recreate a position if he has used one to create it.

and The natural situational super ko rule treats causes and consequences as to prohibition the same way: Both can only arise due to board plays. Thus natural situational super ko is conceptionally clearer than situational super ko that also allows pass plays to cause situational prohibitions. In practice, natural situational super ko and situational super ko have almost always the same outcome, although natural situational super ko sometimes allows unfamiliar move sequences.

X
HermanHiddema: Re: natural situational superko (2008-12-08 17:34) [#5392]

The difference is subtle, and unlikely to affect any realistically played game.

The only difference is that under situational superko (non-natural), you cannot make a move that creates a position that was on the board previously after you passed. With natural, you are allowed to make such a move.

Example on 5x5 board:

[Diagram]
setup  
[Diagram]
play  
  • B1 - last point
  • W2 - pass (stupid, white forgot to defend)
  • B3 - takes ko
  • W4 - pass (no legal moves)
  • B5 - pass (for some weird reason)

Now with situational superko, White cannot capture in the corner, because she previously left that position on the board with a pass (W2). Under natural situational superko, white can take, because leaving a position with a pass does not count, only positions "created with a board play" are restricted.

[Diagram]
setup  

Notice the subtle difference, the marked stone white+circle at a in the first diagram is not in this one

[Diagram]
play  
  • B1 - last point
  • W2 - strang move, white gives black a stone needlessly
  • B3 - takes ko
  • W4 - pass (no legal moves)
  • B5 - pass (for some weird reason)

Now White cannot capture in the corner under either situational rule, because this position was created with a board play (W2), not with a pass.

willemien: Re: natural situational superko (2008-12-22 16:25) [#5424]

thanks copied it to natural situational superko rule (Hope i did it right it was not an instant copy)

 
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