Anonymous: I don't see why white would play in the above solution. I would have expected something like this as the solution. a and b are miai for the kill. If at b, then at a.
togo: Indeed, this is one white ko-threat more than in the book solution. On the other hand in tsumego the displayed opponent's plays are not necessarily the best ones.
Anonymous: For that matter, white seems to die with this continuation as well. I suppose the best solution is the one that leaves the fewest ko threats for white.
togo: That's right, but both after that have one remaining threat.
Anonymous2: But the second leaves a smaller ko threat. (;