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Re: computer-go: Bad interaction between caching and superko?
Scott Roy wrote:
> Robert, can you explain natural situational superko? I think I understand
> situational superko and positional superko, but I don't think I've ever seen
> the term natural situational superko before.
http://home.snafu.de/jasiek/superko.html
Natural situational superko:
"
A player may not use a board play to recreate a position if he has used one
to create it.
"
The rule is not used in practice but in theory it makes more sense than
situational superko because natural situational superko has board plays
for both cause and consequence of rules application while situational
superko allows board plays or pass plays for the cause but only board
plays for the consequence.
Just before a game end with 2 passes natural situational superko is some
fun for a double ko coexistence:
See http://home.snafu.de/jasiek/convent.html for the notation.
. # # # # # O
# O # . # O .
O O O O O O O
b # # # # # O # to move
# O # . # O a we presume some game history where O played the last stone
O O O O O O O and where no ko captures in a or b occurred earlier
(- - = strategic mistake)
#[pp] legal, shortest perfect play
#[aa]# prohibited
#[abb]# prohibited
#[abpp] legal, perfect play
#[abpabpp] legal, perfect play
#[abpabpa]# prohibited
#[p-b-app] legal
#[p-b-apba] prohibited
For a difference between positional superko and NSK see the following:
>>
Date: Fri, 15 May 1998 11:04:00 +0900
From: GGA02126 <GGA02126@xxxxxxxxxxxxxxxxx>
Subject: Re: NSK
To: go-rules@xxxxxxxxxxxxxxxxx
NSK, which only forbids a player to recreate a situation that he
created earlier by playing a stone on the board, seems to allow
the following sequence. Is this the intention of NSK?
+---------+ +---------+ +---------+ +---------+ +---------+
| . # . # | | . # . # | | . # . # | | . # O . | | . # . # |
| # # # O | | # # # O | | # # # O | | # # # O | | # # # O |
| . O O O | | O O O O | | O O O O | | O O O O | | O O O O |
| . # # . | | . # # . | | . # # . | | . # # . | | . # # . |
+---------+ +---------+ +---------+ +---------+ +---------+
(0) (1) (2) (3) (4)
(0) Starting position
(1) White attacks.
(2) Black passes.
(3) White takes ko.
(4) Black immediately recaptures, recreating situation (2).
This is legal by NSK, since Black did not create (2) by
playing a stone.
--James Davies
<<
>>
Date: Fri, 15 May 1998 14:37:17 +0200
From: Robert Jasiek <jasiek@xxxxxxxxxxxxxxxxx>
CC: go-rules@xxxxxxxxxxxxxxxxx
Subject: Re: NSK
> NSK, which only forbids a player to recreate a situation that he
> created earlier by playing a stone on the board, seems to allow
> the following sequence. Is this the intention of NSK?
Like PSK or SSK, NSK does not intend to avoid all particularities
like your nice arcane example. The intention of NSK is to have
consistency of a) causes of prohibitions and b) prohibitions, if a
situational approach is used. Under NSK moves of players cause
prohibited positions and moves of players are prohibited to lead
to positions. Under SSK moves or passes of players cause
prohibited positions while only moves of players are prohibited to
lead to positions.
>>
+---------+ +---------+ +---------+ +---------+ +---------+
| . # . # | | . # . # | | . # . # | | . # O . | | . # . # |
| # # # O | | # # # O | | # # # O | | # # # O | | # # # O |
| . O O O | | O O O O | | O O O O | | O O O O | | O O O O |
| . # # . | | . # # . | | . # # . | | . # # . | | . # # . |
+---------+ +---------+ +---------+ +---------+ +---------+
(0) (1) (2) (3) (4)
(0) Starting position
(1) White attacks.
(2) Black passes.
(3) White takes ko.
(4) Black immediately recaptures, recreating situation (2).
This is legal by NSK, since Black did not create (2) by
playing a stone.
--James Davies
<<
Yes, this is legal and correct play under NSK. As always,
white suffers from a lack of trivial positional ko threats.
We all suffer from the experience with basic ko tradition
and tend to object to allowance of immediate recapture in a
basic ko. There are a lot of ways to handle basic ko
captures after passes including allowance of passes as
ko threats or pass for ko rules. Every solution creates
some kind of strange feeling as far as tradition is
concerned. All said, PSK is simplest::)
--
robert jasiek
<<
>>
Date: Mon, 18 May 1998 12:37:00 +0900
From: GGA02126 <GGA02126@xxxxxxxxxxxxxxxxx>
Subject: Re: NSK
To: go-rules@xxxxxxxxxxxxxxxxx
If NSK doesn't always forbid +---------------+
immediate recapture of a ko, | . O . . . . . |
then the chances of life for one- | O # # # . # . |
eyed groups, while still not | . O O # # . # |
very good, are considerably | O . O # O # . |
improved over PSK and SSK. | . O . O O O O |
Here's another example ---> | O O O # # # # |
In the middle diagram | . # # . # # . |
below, White does not bother +---------------+
capturing Black 1, because Black to play
White would be allowed to
recapture immediately. In the final position, all stones
are alive, including the three white ones in atari, because
as soon as Black does anything other than pass, he loses
the bottom right corner.
+---------------+ +---------------+ +---------------+
| . O . . 1 . 5 | | . O 4 6 # . # | | . O O O # . # |
| O # # # . # . | | O # # # . # . | | O # # # . # . |
| . O O # # . # | | . O O # # . # | | . O O # # . # |
| O . O # O # 3 | | O . O # O # # | | O . O # O # # |
| . O 4 O O O O | | . O O O O O O | | . O O O O O O |
| O O O # # # # | | O O O # # # # | | O O O # # # # |
| 2 # # 6 # # . | | O 2 1 O # # . | | O O # . # # . |
+---------------+ +---------------+ +---------------+
3, 5, 7: pass White passes
Even zero-eyed groups can live under NSK.
+---------------+ +---------------+ +---------------+
| . # . # . # . | | . # . # . # . | | . # . # . # . |
| # # # # # # # | | # # # # # # # | | # # # # # # # |
| O O O O O O O | | O O O O O O O | | O O O O O O O |
| O . O # # # # | | O . O # # # # | | O . O # # # # |
| . O # # O O . | | . O # # O O . | | . O # # O O . |
| O O # O . O O | | O O # O 1 O O | | O O # . # O O |
| . O # # O . . | | . O # # O 2 . | | . O # # O O . |
+---------------+ +---------------+ +---------------+
Black to play Both pass
A variation of the above: Black lives in the bottom
right, but White wins the game by playing stones inside
Black's territory that Black cannot afford to capture.
By NSK, all stones in the final position are alive.
+---------------+ +---------------+ +---------------+
| . . . # . . . | | 4 6 . # . 8 10| | O O . # . O O |
| # # # # # # # | | # # # # # # # | | # # # # # # # |
| O O O O O O O | | O O O O O O O | | O O O O O O O |
| . . O # # # # | | . . O # # # # | | . . O # # # # |
| . O # # O O . | | . O # # O O . | | . O # # O O . |
| . O # O . O O | | . O # O 1 O O | | . O # . # O O |
| . O # # O . . | | . O # # O 2 . | | . O # # O O . |
+---------------+ +---------------+ +---------------+
Black to play 3, 5, 7, 9: pass Both pass
Another NSK feature: after White connects at 1 below,
Black passes, gaining the right of immediate recapture in
the thousand-year ko at bottom left, so White can't win.
+---------------+ +---------------+ +---------------+
| . # . # O . . | | . # . # O 1 . | | . # . # O O . |
| # . # . # O O | | # . # . # O O | | # . # . # O O |
| O # # # # # O | | O # # # # # O | | O # # # # # O |
| O O O O O O O | | O O O O O O O | | O O O O O O O |
| # # # # O . O | | # # # # O . O | | # # # # O . O |
| . # . # # O . | | . # . # # O . | | . # . # # O . |
| # O O . # O . | | # O O . # O . | | # O O . # O . |
+---------------+ +---------------+ +---------------+
White to play 2: pass 3: pass
Under other ko rules, White would win the game by
capturing and connecting the ko after Black's pass.
The symmetry of the NSK definition is neat. NSK's
effects may place it in a slightly different category from
PSK and SSK, but it sheds some light on the way the super-
ko rule works.
--James Davies
<<
>>
Date: Fri, 08 May 1998 20:11:53 +1200
From: W.Taylor@xxxxxxxxxxxxxxxxx
Subject: SSK-NSK
To: go-rules@xxxxxxxxxxxxxxxxx
Hi rulefolk.
Robert Jasiek has asked many interesting questions over the months,
and I believe I can now answer one.
He asked for a position that distinguishes SSK from NSK = where you can
repeat a whole board position if you only *passed* to make it before.
Here 'tis...
X X X O O .
. X . X O O X has a moonshine life at the top.
X X X O O .
:O O O O O O
X X X X X X
X X X X X X
. X X O X X there is a double-ko seki at the bottom.
X O O . O .
O O O O O O
Let's say O has just played at : giving the position shown, with open kos...
x x o X to play; and X passes, giving...
x x o O to play, and O attacks the moonshine,
o x o X to play, and X fights with the double ko,
o x x O
o o x X
x o x O
x o o X
x x o O to play.
With NSK, X can make this last move, because last time he made this
position it was with a pass. Now O can't take anything, so he must
pass, and black's moonshine survives! He wins by 2.
But with SSK, X cannot make that last move, so X loses the double ko.
(Or alternatively he leaves the moonshine alone and saves the double ko.)
Q.E.D.
P.S. This position occurred to me as a result of John Fairbairn's
recent post about the Nyobutsu decision involving this case!
Cheers,
-------------------------------------------------------------------------------
Bill Taylor W.Taylor@xxxxxxxxxxxxxxxxx
-------------------------------------------------------------------------------
"Do not pass" GO = do not collect $200.
-------------------------------------------------------------------------------
<<
--
robert jasiek