Please verify --Dieter
unkx80: It seems to me that shape 1 is alive. If this is true, much of the contents of this page needs to be revised.
1. No outside liberties
In addition, we will assume the marked stones, so as to give Black no escape routes to the outside. In this case, White can kill by playing the obvious placement at a.
After , a and b are miai for the kill:
Less intuitive perhaps is this variation. makes an eye in the stomach. White will eventually be able to fill the inside liberties. If Black does so, his eyespace will become almost filled with a pyramid four killing shape.
In this variation, the outside liberties are important. Black puts up resistance, but White makes an eye in the stomach. She counts the inside liberties for a total of three. Black has only two outside liberties and falls short.
If here falsens the eye.
If White connects with , makes it a seki.
If here, Black makes it ko.
Nope... after , a and 4 are miai.
2. Outside liberties
If Black has an extra liberty, this variation doesn't work anymore. Black lives through capturing a bent four.
If here, now sets up a ko.
Matthew Woodcraft: I can't see a way to kill.
Charles Matthews I believe ko is the correct answer.
unkx80: How about and ?
pitimp?: if black playes 4 at "a", white 5 at "b" is still ko