Cho Chikun's ELD, Intermediate problem 259

[Jhyn]

This is a problem from Cho Chikun's Encyclopedia of Life and Death, Intermediate problems. Black to play and get the best result:



I cannot find a way to kill White. I played out a few of the most obvious variations, with regards to the timing of the throw-in, looking for a ko in the corner. However in all cases White manages to escape. The main variation can be considered good for Black (he takes half of the group in sente), but it seems to me that White's stones on the left were placed on purpose so that this variation doesn't kill the whole group. I assume there must be something better.

I would appreciate your input.

[oren]

[Jhyn]

Thank you very much.