Discuss Spight rules:
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.
Does it mean that a pass of one player can erase the board position history of all players?
Bill: A pass, just like a board play, removes ko bans. :-) It cleans the slate and starts fresh from the current position. (OC, for ending the game all positions where a player has passed must be remembered.)
I think of one bestiary in the 1x8 go board:
A perfect play of should be at a. After that is placed on current . This yields Black winning 3 points. Then what is the consequence of this ?
Black 11 is in the diagram. End result is also +3.
Bill: Thanks, Wilton. That looks right. :-)
If captures another side, you can jump to several graphs later by yourself.Variation 1
Passing White 6 is a must.
This is where the bestiary occurs - now White 8 has nothing to do but to pass. But it helps Black to get rid of her history.
Bill: is banned. It repeats the position resulting from (pass). No pass has intervened since then.
(Passes are treated like board plays as regards ko bans. The same would be true if had been a board play. The superko rule is positional.)
Nothing can be done for White. She passes again.
That's the end of the game. Black wins all 8 points. I just wonder why White's continuing struggle doesn't count (despite the imperfect moves in the past). I don't think Black really has the right to gain all points.
Bill: As it turns out, he doesn't. :-)
However, my rules do not guarantee no anomalous results if a player makes a mistake; in particular, if a player passes in a hot position. The end of play rules are meant to apply when the play is really over, not before.
That having been said, I agree that White's earlier mistakes are irrelevant here.
We could start from this position with Black to play. :-)
Anomaly is in the eye of the beholder, but Spight rules are immune to this kind of anomaly, where the game ends in a hot position (Diagram 2) and no one has erred.
(The only known exception occurs with molasses ko, and arguably that's a good thing. ;-))
I fail to replicate the canonical moves from diagram 1 so that it ends at diagram 2. Could you please kindly elaborate?
Bill: That's what I'm saying. There is none. :-)