How do Japanese rules handle this?
Posted: Sat Dec 07, 2019 3:05 pm
Question: What do the Japanese rules say about this position? Assume the rest of the board is filled too.
Under normal play, if neither side has external ko threats, then white is stable here and will own all of the top because if black captures, white has a local ko threat of throwing in at "a".
Under Japanese rules, does white still need to spend an extra defensive move before the game ends? My "instinct as a Go player" says I want the answer to be no (actually, maybe yes, I'm not sure), but my mechanical understanding of Japanese rules says yes.
My justification: if white does not do so, then white's stones in the upper left corner are dead because they can be captured, and black capturing them does not "enable" any new alive white stone to be placed.
Black demonstrates this by capturing here: White is prohibited from recapturing without first passing for that ko. If white throws in with
it still does not help because ko threats no longer allow one to recapture in a ko. The ko remains, and presumably white is still prohibited from recapturing until passing for it.
So 
passes for ko,
And so white's upper left group dies. So white's group would be dead by confirmation. Black's stones in the initial position would also be dead too, so my understanding is that mechanically we should say that this is an "antiseki" unless white spends an extra move (losing a point) before ending play (or perhaps both players lose since an effective move was needed before ending play).
It doesn't seem to me like the "enable a new alive stone" to be played condition helps either. In the process, white can of course finish off a few black stones by following up at b, but specifically black's final capture of the 5 white stones in the upper left did not "enable" white to play a new alive stone at
or "b" or "a", white could have played those all anyways. This isn't a "snapbacky" position.
The same way that if the game ended here: Then white's upper left would not be considered alive with black having the ability to play "a" and "b", regardless of the fact that white in the meantime could be playing new alive stones into "c" and "d" and "e". In this second position, of course, precisely because white cannot sustain a claim of the upper left stones as alive-as-it-stands, we might have very shortly have "both players lose" due to realizing that they should have continued play rather than passing.
Is there something I'm missing here, or is this how it would work?
Under Japanese rules, does white still need to spend an extra defensive move before the game ends? My "instinct as a Go player" says I want the answer to be no (actually, maybe yes, I'm not sure), but my mechanical understanding of Japanese rules says yes.
My justification: if white does not do so, then white's stones in the upper left corner are dead because they can be captured, and black capturing them does not "enable" any new alive white stone to be placed.
Black demonstrates this by capturing here: White is prohibited from recapturing without first passing for that ko. If white throws in with
it still does not help because ko threats no longer allow one to recapture in a ko. The ko remains, and presumably white is still prohibited from recapturing until passing for it.
So passes for ko, And so white's upper left group dies. So white's group would be dead by confirmation. Black's stones in the initial position would also be dead too, so my understanding is that mechanically we should say that this is an "antiseki" unless white spends an extra move (losing a point) before ending play (or perhaps both players lose since an effective move was needed before ending play).
It doesn't seem to me like the "enable a new alive stone" to be played condition helps either. In the process, white can of course finish off a few black stones by following up at b, but specifically black's final capture of the 5 white stones in the upper left did not "enable" white to play a new alive stone at
or "b" or "a", white could have played those all anyways. This isn't a "snapbacky" position.The same way that if the game ended here: Then white's upper left would not be considered alive with black having the ability to play "a" and "b", regardless of the fact that white in the meantime could be playing new alive stones into "c" and "d" and "e". In this second position, of course, precisely because white cannot sustain a claim of the upper left stones as alive-as-it-stands, we might have very shortly have "both players lose" due to realizing that they should have continued play rather than passing.
Is there something I'm missing here, or is this how it would work?
