The vital point is a. Black lives (without ko) and White kills (in ko) if she plays there.
DaveSigaty: Usually in a problem when we say White kills, we mean without resorting to ko. In this case how does White kill outright after Black 2? I must be missing something - as usual :-)
unkx80: This is a famous classical shape and if I remember correctly, the correct answer is a ko. The manga did not show any variations for this one.
jvt: Yes. I should have checked. This is indeed a very famous problem. It is problem 45 from part 3 of Gokyo Shumyo. There is a slightly different version in Xuan Xuan Qi Jing and Guanzi Pu.
See "Variation at 2" below for another possible move for Black, still leading to ko.
a=10 b=11
a=10 b=11
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Please correct my flawed play? I thought this might be it, but it seems not... could someone also read out the sequence for the proper solution? Thanks!