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Re: [computer-go] Super Ko on KGS ignores player to move

On 8/15/05, John Tromp <John.Tromp@xxxxxxxxxxxxxxxxx> wrote:
> drd@xxxxxxxxxxxxxxxxx wrote:
> Dear Don,
> Let me explain in greater detail why I believe there are very
> good reasons to prefer PSK over SSK.
> Your basic argument against PSK is that the simple notion of
> position doesn't entail everything that matters for the future.
> While I agree that is correct, I want to argue that the notion
> of position should *shouldn't* entail additional information that
> matters for the future.
> Why? because it cannot be taken to its logical extreme.
> Consider the position
>  X . X
>  O X X
>  . X X
> with white to move. I ask you, do you care which color you are assigned?
> Then you say, well, that depends on whether O is allowed to capture the ko.
> Reflecting on this, we can see that in fact the entire history matters
> as to which color we prefer.
> At the same time it is entirely obvious that a SUPERsuperko rule that takes
> the whole history into account is useless.
> The conclusion we must draw as that trying to include information about
> the future into the notion of position is inherently flawed. I consider
> any solution that includes some information while excluding other information
> to be a compromise at best.
> Choosing the simplest notion that does what we want in practice seems the
> best solution then.
> It is both easier to describe and easier to implement (at least conceptually;
> there is one set of forbidden stone configurations, rather than two separate
> sets).

I must say I don't understand the explanation above. If you want to
forbid repetition (endless or otherwise) you need at least some of the
game history to decide whether that happened or not.

The question is: repetition of what. Obviously repetition of something
you consider the 'state' of the game. PSK considers the state of the
game to be the position of the stones. Don argues you might as well
include the color to move as it's a rather vital piece of information.

I don't think it's conceptually different or more complicated, either
to describe or to implement, it's just that one description of 'state'
includes color to move and the other does not.

But I must say the difference between PSK and SSK is small and maybe
arbitrary. It's just that intuitively the color to move is part of the
state, as the question where to move in a position makes no sense
without it. And for that you need no ko.
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