Taw: How about this ?
Hikaru79: This ends up extremely bad for black. White lives with either two prisoners in gote or one prisoner in sente.
How about this?
unkx80: Both diagrams are wrong.
Malweth: My try
unkx80: Good try, but unfortunately , and are wrong moves.
ChrisSchack: Next try, I guess. Of course, your comment about move order is a dead giveaway...
This leads to ko, I think, and if B has enough threats. In place of , W can't simply connect at as in the diagram below, else:
and now it IS a ko for life. Therefore, W would have to play so as indicated in the next diagram, in place of above.
Without the black stone at a, can extend and say arigato to Black for the free gift. Obviously White should not play at b otherwise black can play at and thank White instead.
On the other hand, with the marked stone, is not good, as starts a one step ko compared to a two step ko in the solution.
So without Black a, Black should atari at . The correct response is , irregardless whether there is a Black stone at a. I believe this is probably a IGS 1k* level indicator.