Solution by lavalyn 17k:
Black takes the corner for eye space. Now the best White can do is to minimize the eye space available, but the available space is sufficient to ensure life.
For your viewing pleasure, some failure diagrams:
Black, in his attempt to take more of the side, loses after and
: on the second line, six die but eight live.
What's wrong with white trying here?
It seems that black must ultimately play to the right of , but he cannot avoid filling in his own eye:
and black dies as before. How can black respond?
--satyreyes?, unknown rank but probably very, very low
For your further viewing pleasure, some not so minor changes to the problem (by Sergio) :
If the stone is on the second line (instead of the third) Black is dead...
But what should White play in answer to a ?
Even if it's not a clear move to beginners is the only one that kills.
Deebster: Doesn't b kill Black too?
unkx80: Yes, b kills too.
If Black attempts to capture with , White plays
to prevent an eye at
. If Black captures at
, White plays at
, the vital point of the remaining straight three.
But what if Black plays ? White plays
to take away the last chance for an eye. Capture
any time to kill the group.
So we can conclude that in the original problem, Black's threat of escape along the second row is necessary for survival. With present, that threat disappears, and White can hane with impunity.