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:
Black looks pretty dead if he just connects to avoid the ko.
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?
W need only ignore a single threat to play a, winning the ko. No need to connect to the other side, they're already alive. B has a direct ko, but has to make the first threat.
On second thought, why not take , it's extra points...