Re: [pbmserv-dev] proposed ko algorithm for pbmserv go

[Randall Bart <barticus@att.net>]

'Twas 06:18 PM -0700 on Friday 9/5/2003 when Scott Huddleston wrote:
> First:  confirming the general ko rule.  Is it that no exact position
> should ever be repeated?

Not the way I learned it.  The ko rule as I understand it is simply that 
you may never make a move that exactly undoes the prior move, eg, if after 
move 102 the board is exactly the same as after move 100, that is ko and 
that is an illegal move.  There is no rule barring repeating an earlier 
position.

If there are three ko situations on the board, it is possible for us to 
loop through those forever (I take A, you take B, I take C, you take A, I 
take B, you take C, ad infinitum).  In such a situation, the game is a draw 
if neither player wishes to leave the loop.  Generally the player who is 
winning will break out of the loop, but if neither player can break out 
without losing something it can be a draw.

While ko occurs multiple times per game, triple ko and other repeating 
situations are very rare, so the gods of Go have never chosen to make a 
rule for it.

The program code to detect ko shouldn't be too hard.
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