Zephi: This one seems a bit complicated, but I can see at least two possibilities. Focusing on only the two marked stones, white needs B to keep them from escaping, but can't play there without being immediately captured, so I think white would have to first set up a ko at point A. After this, I think that B and C are miai for capturing, though white would need some good ko threats to make B work. Here's how I think both cases would look:
In this case, black takes first in the ko, so white needs to have some really good ko threats to make this work.
Again, Black takes first, and white needs a very good ko threat. ( seems like it would only cause black to fill in the ko in which case, playing at c is no longer an option for white.)
Well, if this isn't the solution, I hope it's at least on the right track.
Malweth: Going with your last diagram, White does take ko first. If instead elsewhere,
at
kills.
unkx80: Sorry, but Zephi's solution is correct. In your diagram, can connect, but
cannot play at a without putting himself into self-atari.
Malweth: I'll take the easier path (I think...)
unkx80: I would say, White's play is sub-optimal. But you are almost there already. =)
Malweth: I see, I think... White would do better to save the E19 group.
ChrisSchack: I think looks odd in the two-step ko ... why give B the chance to take first?