In message
<72e25bef0904140750n7776a8a4xb96bdc7cd34d5...@mail.gmail.com>, Richard
Brown <batma...@gmail.com> writes
2009/4/14 Brian Sheppard <sheppar...@aol.com>:
But in game 739216 the stones are the same, but the other color is moving.
That can't be a repetition...
Well, that's what distinguishes _positional_ superko from _situational_
superko. See <http://senseis.xmp.net/?Superko> .
As Jason House wrote,
That sounds like a classic _positional_ super ko violation. Any board
repetition is a ko violation, regardless of the player to play.
_Regardless_ of the player to play. [Emphasis mine.]
Now, one might have _philosophical_ disagreement about whether
that's the way a server "should" implement a prohibition on cycles,
or about whether that's "what the framers intended". And I might
even agree with you that _situational_ superko is "superior" in that
regard. Under situational superko, your example, as you say,
_can't_ be a repitition. [So, one might well ask, what is the reason
for prohibiting it?]
But whether we like it or not, that is how the server authors have
chosen to implement the prohibition (even though allowing the
_other_ player to play in the position would not really create a
_cycle_, in the sense of a "directed acyclic graph").
[See <http://en.wikipedia.org/wiki/Directed_acyclic_graph>.]
Situational superko can be defined in terms of not permitting a
cycle in the game-tree, thus always preserving its acyclic nature.
[Positional superko, IMHO, has no such elegant rationale.]
But postional superko is what both KGS and CGOS implement,
and we have to live with that, at least until they see the light.
It's not a matter of "seeing the light". I am sure that those who have
considered the issue have realised that Situational Superko is better
than Positional Superko (and probably, that Natural Situational Superko
is better than both). However, the "Chinese rules" setting on KGS
attempts to implement what the Chinese rules specify; and this is
Positional Superko.
According to Robert Jasiek, the writer(s) of the Chinese rules did not
intend to specify Positional Superko. The intention was to have the
ordinary ko rule, with also a restriction on the "sending two capturing
one" cycle. It is this cycle which I think caused the problem in the
game cited by Brian at the start of this thread. So even if the Chinese
rules said what they were meant to say, they would forbid the move cited
by Brian.
Nick
--
Nick Wedd n...@maproom.co.uk
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