[1] O19, success
[2] M18, success ?
[3] Q19, failure
PeiweiCao Now White has two choices:
Black lives.
Or...
One of the two blocks of White will be eaten, and Black lives.
[2] Alternatively:
I think the solution is the following:
White is 10 is played anywhere, and black lives on the next move.
What?
White connects, black is dead.
[3]
YongCao? I think should play first, then
.
PeiweiCao Black dies:
PeiweiCao: Consider white move 2 at p19 instead of m18, I believe that white p19 assures the death of the black corner.
unkx80: If , then the tesuji of
and
should ensure life.
Alexandros? Not a very good player here, but I think PeiweiCao's method fails to the following:
Then, as I read it, if black picks this path: (with move 3 filling in the liberty)
unkx80: at
?
Alexandros?: I'm not sure if it's cheating in a problem, but we could play at
in that case, and run into the wall at the other end of the board. Of course, this goes beyond the bounds given for the problem, so it may be wrong...
unkx80: By the usual conventions in life-and-death, we assume that the rest of the board is empty, so feel free to extend the diagram as you wish, so this is not cheating.
For your question of at
, I leave it as an exercise: What is the gist of this problem? The tesuji has been mentioned on this page at least twice already...