Probably safe to say that this is a problem which most people here have never encountered. It comes from a rare Ming Dynasty weiqi manual which only has words and no diagrams. Quite an interesting problem. You will need to look for the strongest line to find the right answer. Have fun.

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http://tchan001.wordpress.com
A blog on Asian go books, go sightings, and interesting tidbits
Go is such a beautiful game.

Aha! Nine Old Men is the clue. Relieved to see this old man can still remember some things.

I came across a problem that looks very similar to this problem. According to the commentary, the solution is intended to be unconditional kill, but subsequent research indicates that black can get a ko.

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My homepages: http://senseis.xmp.net/?Unkx80 and http://yeefan.sg/.

It wouldn't be the first time I've heard of ancient problems having a solution as ko after subsequent research. I wouldn't be strong enough to show refutations anyways. I only have the main line from the ancient text.

_________________
http://tchan001.wordpress.com
A blog on Asian go books, go sightings, and interesting tidbits
Go is such a beautiful game.

BTW, B4 under 1 doesn't work in unkx's diagram.