All known forced Go cycles are impossible with this rule. The nature of the rule itself suggests that forced cycles are either impossible or astronomically rarer than they are in Go when the superko rule is not used. Ko fights proceed in a similar way to those of Go, with the difference that captures and moves answered by captures aren't valid ko threats. On the other hand, snapbacks are not possible. Under the unrefined rule, it is necessary to make a ko threat before any consecutive capture occurs.
If a play causes a board position to be repeated, the game will end in a draw. If forced cycles are indeed impossible, this will require cooperation between the players, which shouldn't occur in actual play.
Luis BolaŮos Mures designed Stoical Go in September, 2012. The game is available to play with the Zillions of Games program. All odd-sized boards from 7x7 to 19x19 are implemented, as well as the option to use neutral blocking pieces to change the shape of the board.
Refining the rule to explicitly allow snapbacks still prevents all known forced cycles. A few such alternative rules follow:
- If your opponent captured n stones on his previous turn, you can only make a capture on your turn if it's bigger than n stones.
- You can't make a capture on your turn if your opponent just made one, unless they captured exactly one stone and you're capturing more than one stone.
- You can't make a capture on your turn if your opponent just made one, unless both captures together constitute a snapback. A snapback is defined as a capture of a single stone by extending an already existing group followed by the capture of said capturing group.
Here's a similar replacement for the ko and superko rules that also prevents all known forced cycles:
A player can't place a stone inside an enemy territory if the opponent made a capture on his previous turn.
For this purpose, the word "territory" is used in its strict sense, i.e. a maximal set of orthogonally adjacent empty points only constitutes an enemy territory if no point in it is orthogonally adjacent to a friendly stone.
Snapbacks can also be explicitly allowed here without reintroducing forced cycles into the game.
tapir: You are aware that you will have many "right to capture" fights? Even snapbacks are impossible in your variant.
luigi87: Not that many, but yes, often a player will have to use a ko threat in a given sequence to earn the right to capture back. The same happens with snapbacks as well. This feature adds a global positional factor to the evaluation of local fights, which needn't be a bad thing. As for snapbacks, I've added a few alternative rules that preserve them in their original form (i.e. without the need for intervening ko threats). (I had thought they didn't work because of Molasses ko ónot a cycle in itself, but potentially part of oneó, but that one also contains captures that are smaller than the preceding capture, so it's not a problem.)
luigi87: Eternal life is not possible in Stoical Go. in the entry's example sequence is an immediate re-capture.
Sandra: Counter example:
Slarty: This is not a forced cycle, so it doesn't disprove the claim.
Sandra: The other claim was that standard ko rules donít apply. Thatís the claim thatís disproved here.
luigi87: "Standard ko rules don't apply" is not meant as a claim, but as a rule of the game, as in "standard ko rules aren't used". Maybe it's a bad choice of words. Is it? If so, I'll change it. Needless to say, I'm not a native English speaker.
This said, ko rules aren't needed, by which I mean that there are no known forced cycles so far which make them necessary when the game is played to win.
Slarty: It's still (technically) needed to know what happens if a repeating position is played, to define the game. It could be a source of a little confusion though I think the page is clear. (would imagine borrowing chess's threefold repetition = draw in a very thorough description). Anyway, the game should be pretty good. It's difficult to make it the same as Go (in under ten words, at least) - because there can be snapbacks of any size.
A funny variant idea (doesn't need its own page) is to forbid the last player who captured (or the one with the most prisoners) from capturing again. It's sort of like the doubling die mechanic in backgammon.
luigi87: Yes, it reminds me of a set of bizarre finite Go variants that I discussed a while ago on Life In 19x19. In the most basic one, once a player makes a capture for the first time, that player canít create any more groups for the rest of the game. It creates an intriguing build up of tension prior to the point when one of the players decides to make a capture. As for repetitions, you're right. I've just added a rule to handle them.
This variant is a little similar to one variant related to simultaneouness I was thinking about, that was this: White cant move to a place that had an piece on previous turn and cant capture an piece that was included on previous turn or that make an group with a piece added on previous turn. Game end after 2 consecutive passes if the last pass was a white one, or 3 passes (white pass will still be the last one.