luigi wrote:
Quote:
(if KoRule is Simple): Additionally the game also ends if:
A player passes from a state that the player has already passed from once before.[4]
[4] This Spight-style termination condition ensures that sending-two-returning-one-type positions will terminate, even under area scoring where the cycle does not "cost" points.
A player passes from a state that the player has already passed from once before.[4]
[4] This Spight-style termination condition ensures that sending-two-returning-one-type positions will terminate, even under area scoring where the cycle does not "cost" points.
This seems to be used when Chinese-like rules are selected as well, but doesn't it make sending-two-returning-one play out differently? I think Chinese superko (which forbids 3-play cycles) should be included as well.
Yeah, I agree it's not an exact match. I'm a little sad though to implement fourth/fifth/etc ko rule to select between. It seems to me that in practice, Leela Zero already works usually fine for Chinese rules despite having several differences, one gets even closer by forbidding suicide and using Japanese simple ko. At that point, it's not really in a player's interest to try to waste time in a sending-two-returning-one in the first place - the main reason you'd ever try it was only if it somehow kept the game from terminating.
Maybe it's worth adding, still? Also, is sending-two-returning-one actually the *only* 3-move cycle? My understanding was that Chinese rules prohibit sending-two-returning-one cycles, not 3-move cycles, in which case it matters if they are the only one.
Matti wrote:
lightvector wrote:
Did you have any tricky cases in mind involving either this, or the proposed change to unblock all moves for either player that aren't ko-moves, rather than just those of the opponent?
Quote:
Black seems to be dead.
...
Is this what we want?
So we have "current" rule: only unblock opponent non-ko-moves after your move.
And "changed" rule: unblock all player's non-ko-moves after your move.
Under the changed rule, if you notice in your example,
unblocks black's ability to capture 
because for a brief moment, everything of white is in atari. So black is actually the one winning because black can continually recapture everything without spending turns to unblock, whereas white cannot.Under the current rule, your example seems to make sense, but I think black makes an error. Black should not capture at
, instead black should unblock taking . Then after 
, black takes and becomes safe. Black can then just cycle forever using the 3 ko mouths, always one step ahead of white, always refusing to take the second-stage ko.So there are four ways this can play out - black first current rule, white first current rule, black first changed rule, white first changed rule. I think this gives:
Current rule: black first is safe but white can force no-result if white is losing and black cannot give up the group and still win. White first kills black.
Changed rule: black first kills white, white first kills black.
Do you agree with this? If this is correct, then there is some difference, and is not clear how to handle it, but if anything, the changed rule is a bit more symmetric here.
Usually, I think we will not get to cleanup phase with this situation in the first place though. In normal play, either player can force a no result by insistently capturing the ko mouths over and over if their opponent is unwilling to sacrifice their whole group, so whichever player would lose, if they are losing by less than the value of the whole fight, can do so. I think this is generally true of situations where two groups share tons of ko mouths and have no other liberties, so I'm less worried if this kind of situation differs between this formalization and "true" Japanese rules. Actually, I don't really know how "true" Japanese rules would handle this situation either if somehow the game ended during main play without either of the players having attempted to force the no result.
What do you think?
to the left of 
.
