Delayed suicide
There are several ways of dealing with the concept of suicide, the situation where a player creates a chain of his own stones without liberties. Some rules disallow suicide altogether, some allow it by removing the chain. Delayed suicide provides a third option. It is in some ways simpler than either of the other options, as it requires no real additional rules, but is the result of the following rules:
- A player may play a stone on any empty intersection (barring ko).
- After a player has placed a stone (or passed), all opposing chains without liberties are removed.
(note that removing the word "opposing" from the second rule leads to the Simultaneous Capture rule)
Example:
Black plays . This is allowed, as the intersection was empty. No stones are removed at this point, as there are no opposing chains without liberties.
White plays elsewhere. Now,
and the
marked stones are removed, as they are now an opposing chain without liberties.
In effect, the removal of the black stones is delayed until white's next move, hence the name delayed suicide.
Note that this rule makes it possible for a chain without liberties to remain on the board briefly.
Effect on strategy
Delayed suicide can be used strategically in some situations to achieve a different result from that in normal go. One such situation is oshitsubushi:
With rules that disallow suicide, is not allowed and white is unconditionally alive.
With rules that allow suicide, is a ko threat, as it removes the black stones and thuse requires white to play at the 1-1 point to live.
With delayed suicide, seems to kill the group, but white can save it with a (large enough) ko threat.
If white simply plays elsewhere, and the marked stones will be captured, after which black can play
at
to kill the group.
To prevent this, white can play in a way that requires a response from black (i.e. a ko threat). After black responds to white's ko threat with
, white can then play
at
to live, as the black stones were removed after
.