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Spight Rules
    Keywords: Rules

I have proposed these two rules which address the questions of endless repetition and stopping play at the end of the game.

  A board play may not repeat a previous whole board position
  unless a pass has intervened since its last occurrence.
  Play stops when the same player passes a second time in the
  same board position.

With area scoring play ends when play stops. With territory scoring play stops twice. After the first stop there is an encore in which a pass costs one point and each player makes the same number of plays (considering a pass a play). Also, passes before the encore do not count for stopping play in the encore. After the second stop play ends if each player has made the same number of plays. If not, the second player in the encore makes an obligatory pass and play ends.

/Discussion

-- Bill Spight


{Explanatory discussion under construction.}

Spight rules are based upon the idea of evaluation. First, play should stop in a position that has a definite value (score). Second, the score of such a position may be determined by play with passes that have a value.

Using passes to evaluate positions is based upon the idea that if one player makes a play that gains a certain amount, and then the other player makes a play that gains the same amount, the result is the same as the value of the original position. If we treat a pass like a play and the value of a pass is the same as the value of best play (under these conditions) in a position, the resulting position after a sequence of best plays and passes with the second player passing last will have the same value as the original position.

[Diagram]
Half point

By convention the framing stones are alive. We count the Black territory in the corner as 1/2 point. (OC, at the end of the game it will be worth 0 or 1.) The miai value of a move at a is also 1/2.

Suppose that the value of a pass is 1/2 point, that Black plays at a, and then White passes. Black gets 1 point in the corner but White gets 1/2 point for the pass, so the result is 1/2 point, the same as the original value of the corner.

[Diagram]
Ko

Here the corner is worth 1/3 point, and the miai value of a play is also worth 1/3 point.

Suppose that passes are worth 1/3 point. Then Black may take the ko, White passes, Black fills the ko, and finally White passes. Black gets 1 point for the captured White stone and White gets 2/3 point for the two passes, for a result of 1/3 point, the same as the original value.

Note that this works only if White's first pass lifts the ko ban, just as a board play would. Otherwise Black is not obliged to fill the ko.

All of this, of course, depends upon the value of a pass and the value of a play being the same. If passes are worth zero, and plays are worth zero or less, correct play in this environment of passes will not change the value of the position. The value of the position will remain the same. Thus, we can say that the position has a score.

Of course, it may be possible to calculate a score for some non-terminal positions, but only some positions are such that that calculation would produce the same result, even if play were to continue. Only such positions have a constant value that coincides with the score. They are scorable.

By area scoring, if we treat each stone on the board as alive, we can count one point for each stone on the board and one point for each point of surrounded territory. If some of the stones are dead, the result of that procedure will not be the value of the position. Provision may be made to remove dead stones by agreement, but continuing play should also lead to their removal, to reach a position with a constant score.

In the next example, under some area rules the game may end in a position where the current result is different from the one if play were to continue.

[Diagram]
What result?

This example is a variant of one of Ing's. White to play.


[Diagram]
Diagram 1

B4 = pass.

By AGA rules and some others, White can now pass and win the game by two points.



This result has its defenders, but it is anomalous. The game has stopped in a hot position in the middle of a ko fight. It does not have a constant value.

Under Spight rules play continues. Black's pass has lifted his ko ban.

[Diagram]
Diagram 2

[Diagram]
Diagram 3

[Diagram]
Black wins

Usually rules differences produce small score differences. Here the difference is 27 points.



Since Wilton Kee has shown how his rules apply to the 2x2, I am following suit.

[Diagram]
Greedy Black

With area scoring, Black may get greedy and try to win by one point. (This is possible under some rules, I believe.)


[Diagram]
W6 = pass

[Diagram]
B9 = pass

[Diagram]
W2 = pass

Note: If B1 were in the top right corner, White could pass and end the game favorably.


[Diagram]
B5 = pass

Now Black is in a dilemma. No matter where he plays, White can pass and end the game favorably.

So Black loses if he passes at move 15. Instead,


[Diagram]
Black takes

[Diagram]
White takes

[Diagram]
Game ends

W8, B9, W10 = pass.

Since neither player can make headway, they pass, ending the game as seki. (Note that Black loses by 2 under territory scoring.)





This is a copy of the living page "Spight Rules" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.