After the cut at , and are forced. White bends at , and Black can only save his group by setting up the ko with and . This is a picnic ko, difficult for Black when White takes first.
The hane at does not work. The diagonal move at is a tesuji which results in double damezumari for Black, so the Black group is cleanly captured.
So, if the top sequence results in ko for the black group, how would White play if Black responded to with ?
Ah, I see now. endangers the upper left group; I was focusing too much on the lower right ^^
HolIgor: On a side note, aren't we missing a stone in the upper right corner?
unkx80: I copied this from KenshinM4, so only he knows.
KenshinM4: I don't think that we are missing a stone. What would make you think that?
unkx80: I guess HolIgor is thinking that the upper right is missing a Black stone because it is exactly the weak carpenter's square.