Moonshine life refers to a position where a (seemingly) dead group with a false eye in ko cannot be captured, because the owner of the group has an unlimited number of unremovable ko threats.
An example position is given below. The question here is: What is the status of the white group in the upper left corner, given the presence of the group in the upper right?
This is the subject of the earliest known Rules Dispute, involving an ambiguous pronouncement by a Japanese monk called Nyobutsu. (John Fairbairn has written about this dispute in an article for Mindzine.)
Modern professional rulesets agree that Moonshine Life is dead. However some rulesets allow other possibilities. Moonshine Life may be considered:
- Dead - one eye dies.
- Seki - White cannot make two eyes but Black cannot kill, because White has infinitely many unremovable threats.
- Alive - the white stones cannot be captured, so the "eye" should be worth 1 point.
- No result - if Black insists on playing the ko, a triple ko occurs
|Table of contents||Table of diagrams
Moonshine Ko, 1
Moonshine Ko, 2
Self-contained Moonshine Life
Internal Moonshine Life
How it works
Now, White retakes the ko with . Black could, if he wanted to, then play , forcing , and returning to the original position. After that, black could start the cycle again by capturing in the upper left.
Note that is prohibited under super ko. So under rules using superko, white cannot win the ko in the upper left, because the white group in the upper right will die. After , if is prohibited, the white group in the upper right will be captured, and since that removes the source of the unlimited ko threats, the upper left can then be killed as well.
Status under Japanese Rules
Bill: By Japanese rules Black waits until the suspension of play and, in hypothetical play to determine life and death, takes the moonshine ko. White cannot take it back except by a pass for it, and if White does so, Black captures White's group. So the group is dead.
It is true that White can cause problems in the hypothetical play by taking in the double ko seki, forcing a Black reply, and then passing for the ko Black took in the double ko seki. To protect himself Black must pass for the ko White took in the double ko seki, and does not have time to capture White's group in the top left corner. In theory, White can keep this up indefinitely. It is a known flaw in the Japanese '89 rules.
jann: This flaw not necessarily exists, it may be simply a misunderstanding of the PassForKo rule. The rule forbids recapture in a ko that the player have not passed for, but it doesn't clearly require a new pass for each later recapture in the same ko.
Herman: Addendum: the same is not true for the self-contained version. In that position, if white takes at a, and black exchanges the ko-threat and response in the double ko, black's whole group will still be in atari, and black is out of options.
Self-contained Moonshine Life
This is another position which falls under moonshine life, except this time it is self-contained. Because of the unlimited ko threats at the marked points, white can never win the ko at a, and so can never capture black.
Again, under superko, the black group cannot win the ko and is dead.
luigi87: This looks more like a triple ko to me.
Bill: If White starts the ko it is a triple ko. If Black starts it it is a double ko.
Internal Moonshine Life
Even if all kos are internal the extra eye makes this a moonshine life and not a real triple ko.
B is safe and can play away. Alternatively, he can also initiate an endless capture attempt. W on the other hand can only flip a ko once and then forced to tenuki or pass.
Moonshine life (which is dead under most rules) can look similar to a valid triple ko (which can lead to draw on repetition) or to an approach ko. It has the following features:
- There is a one-sided repetition potential. The dominant side can start/stop/pause/resume an endless capture attempt at will. The other side can only flip a double ko once then have no other move but pass or tenuki.
- The position is temporarily stable as is. The dominant side never needs to capture the moonshine stones for his own safety (not even eventually, after dame fill). The question is only about L/D and points in scoring.
- There is a one-sided moonshine ko. The dominant side strives to take-and-fill in this ko (which would resolve the situation in his favor). The other side uses further kos to prevent this, but himself cannot and doesn't try to fill any - he needs all of them to barely stay on the board.
The first property is probably why a moonshine position is considered dead under most rules. Would it be considered alive, the game would shrink into a half-game. The dominant side could still win but couldn't lose anymore (just start repetition if fell behind). Korean rules are a notable exception: since they consider L/D locally they treat local moonshine variants alive, accepting the above consequence.
This one-sided repetition is also the reason and the method it can be captured under superko. (Once he attempts the capture, the dominant side also needs to use and disturb in the double ko himself, otherwise he even risks losing the double ko seki.)
The second property is a significant difference to a triple ko, and is also essential to distinguish moonshine positions from an approach ko:
It seems to me (HoverSink?) that of the four options listed, we only have to consider #4.
Since Black can always insist on playing into the triple ko, the position must be treated according to whatever rules we happen to be using for complicated ko. If we used any other reasoning to come to a different conclusion, we would be forced to then change our ko rules in order to keep the game self-consistent.
So, by Japanese rules, would probably result in a voided game. Using a superko rule, would not even be allowed. This problem would then be like the eye shapes reducible to the bent four in the corner; White will eventually become exhausted of all external ko threats, and be powerless to stop Black from playing the ko and winning.
So, in other words, since I am much happier seeing groups dead than alive (so long as they aren't mine), I would probably call White dead.
Tderz to HoverSink?: Also options 2 and 3 are possible (perhaps only under Go-rules where you play it out).
Imagine Black had won anyway (say by B=z+komi+y+a+b+c points), even without capturing the white stones. Then it is better for black to offer White (or the referee) options 2 or 3.
z is = 10 here in this (smallest?) example and would be much larger in most games. (uncorrect: y is partly included in z in my discussion)
By not forfeiting the game by triple ko, black wins it straight away.
Option 2 can be subdivided into two further cases:
Does either player want to fight over ?
2a) If Black does not need it, y above seems to be y = 1.
2b) Either player needs it => Rules questions? Triple ko escape for white? ... for Black?
3) White claims to be alive
3a) White claims to be alive and claims the point at a.
3b) White also claims the point at b.
The value for b had to be b = 1 in order that B can avoid rule type discussions
Value c is for possible Rule-depending points from the other cyclic or seki positions on the right or elswhere, helping to create the problems. c won't exist under Japanese Rules.
1) White must be dead as is:
B=z+komi+y+a+b+c = 10+6.5+0+1+1+0 = 18.5 points.
Black is most probably < 12 points down on the board.
Black had to be 18.5 points ahead to avoid all types of discussions.
2) White can be allowed seki:
2a) B=z+komi+y+a+b+c = 0+6.5+1+0+0 = 7.5 points.
3) White can be allowed life:
3a) B=z+komi+y+a+b+c = 10+6.5+0+1+0+0 = 17.5 points.
Black had to be 17.5 points ahead to avoid all types of discussions.
3b) B=z+komi+y+a+b+c = 10+6.5+0+1+1+0 = 18.5 points. Black had to be 18.5 points ahaead to avoid all types of discussions.
The discussion becomes more interesting and less hypothetical if the colours are inversed:
Now even 3b) becomes W=z-komi+y+a+b+c = 10-6.5+0+1+1+0 = a mere 5.5 points. (a difference of 13 points? I counted komi twice? I give up, it's too confusing in this little window; perhaps I should have taken one reference only, where all left corner stones are dead)
By the way, I feel moonshine life is a beauty. If it is accepted as either seki / alive, we can tell new Go players something like:
You generally need to live locally (eg having 2 eyes). But there is indeed 1 special way to live - live globally! You are sealed in a small place. Not enough eye-space, not live with (ie seki) your besieging group. But you are seki with the whole board.
I think it requires sophiscated skills to set up and make moonshine life. And the occurrence of this makes Go more attractive and complex :-P.
I would like to grant a seki to this great player! "Dead" or "no result" is simply a vote to discourage this marvellous skill.
A passionate comment anyway :)
iopq: Well I think it's dead because, otherwise, what's stopping white from claiming all corners and sides with false-eyed groups? In fact, by the Ing Ko Rule white is dead because she can't keep Disturbing Ko.
Curtmack: Based on what iopq said, I'd rule no result, if I had to. As long as either side refuses to break off the kos, I can't think of any reason not to call it a triple ko. Of course it wouldn't matter if superko rules are in place: whoever runs into the superko first loses.
Chris Hayashida: Does anyone know where the term moonshine life came from?
Bill: I believe this is the Chinese: 假生 (From the Ing rules at http://go.yenching.edu.hk/yingrule.htm ). Altavista translates the characters as vacation life. Perhaps Davies coined the term moonshine life.
MrTenuki: As in the case of 假双活, the character 假 here takes the 3rd tone. Thus 假生 means "false life" in this context.
Bill: Ah! Thanks. :-)
I just ran across this phrase, too. 雙劫假生 . I'm not sure, but does it mean double ko false life?
The Chinese rules also say 假生
SoRight?: So if one disallows triple Ko(three active Ko yield a draw) then a cunning player who has lost a game may be able to introduce enough Ko's with enough territory at stake, and if the winning player isn't wise enough to resolve the Ko's in a timely manner then the result is a draw.
Bill: I am not sure what you have in mind, SoRight?, but the triple ko in Moonshine Life is not fightable except at the end of play, because one player has no threat except to leave the triple ko on the board.