Solution by lavalyn 17k:
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
Bill: If , . Then if , , etc.
rokirovka: As a beginner, I find it helpful to show the shortest variation that proves the black group is alive. threatens to create two eyes in the corner. White plays to reduce Black to one eye in the corner. But now Black plays capturing and . After , Black plays at , creating a second eye at , and the black group has two eyes and lives. If White plays at , Black plays at and lives.
Also, I find it helpful to show the shortest route to life for Black if White plays at . Black cannot play on the first line immediately: If at , at reduces Black to one eye in the corner, and if at , at takes away the point Black needed for his second eye. So Black extends along the second line with , threatening to play next at , which would guarantee unconditional life in the corner with a straight five. So is the only try to kill Black. Then Black extends again with , again threatening to play next at with a straight six and certain life. So is the only try to kill. Now Black can finally play on the first line: threatens to play at and make two eyes in the corner. reduces Black to one eye in the corner, but now captures and . After , at makes a second eye and Black lives. If White plays at , at also makes a second eye and lives.
So it seems to me that if White had a stone at in the original diagram, would kill. White could then play at , and Black is dead with only one eye in the corner.
Elgoran?, 16k: Actually, Black can and will play after . Playing just gives Black another prisoner because of . If White a, Black b and vice versa.
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 plays at a, White kills by the throw-in at .
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.
fred : would Black live with ? And is the rest realistic?
Charles No, should be at .
k, i get it