Most Difficult Problem Ever

Bob McGuigan: In another amazing whole-board problem, composed by Dosaku or perhaps Dosetsu, Black captures 72 stones but is unable to make a living group. I don't know of an online source but it is given as problem 20 in Nakayama Noriyuki's Treasure Chest Enigma.

f3etoiles It is online, on the site of goproblems.com, and Nakayama attributed it to Dosaku (but he may be a little bit biased in his judgment :-)) While we are on it, the same site has also the Dosetsu problem (with a Java solution, but I believe there are some mistakes in it, and it doesn't show the 1 point victory), and another incredible full-board thing, called No Man's Land.

Possibly the ultimate "most difficult problem ever" is: starting from an empty 19x19 board, Black to win. Currently nobody has the solution, otherwise Go would be a solved game. This problem is also often circulated as a joke.