Benjamin's solution was quite convincing by the beauty of . Seeing might spoil the fun, hence I will moved it to /solutions.
These are illustrations of the thought process of a weaker player (me).
tderz: is wrong.
Illustration of White's Ishinoshita: White will live with 11 points.
The usual shape attacking point will not work due to the 3 liberties will have after capture (White can reply with ).
White could have previously exchanged for this - still to no avail.
Black takes first with a, , Black b.
I realize this has already been solved but id like to give it a try with a diffrent solution.
How about that? -- Intetsu
White plays at the point above . After black captures 5 stones, white makes a ko. -- JuhoP
Black to play...
revo: Thanks a lot for your reports, it's very interesting. I tried a little with your tsumego and I think this solves it.
If white does not capture with , black may have to capture the left part of white. Black must not capture at himself, because white can recapture with the marked stone.
Hwan Kuk Kang: Not bad!
maruseru: I got the same solution as revo. Being 9k (EGF), I thought this was rather easy. So the other tsumego (which you got as tests) were much harder?
Benjamin: Yes, I think they were much harder - maybe we can show you one from our test next time... By the way, did you understand why this move ( in variation 2) is wrong?
maruseru: Because of the continuation shown in these three diagrams, which only leads to ko?
Hmmm... at second thought, maybe this isn't a ko. White takes, and Black connects to the right of 9, leaving White with a false eye. Must think some more.
revo: I think you're right, it is ko. If black connects to the right of 9, white captures black 5 and lives.
This looked like a simpler solution to me:
-- TerryMcIntyre, 9k
xela: There's an interesting variation here: