This is a failure diagram from Gokyo Shumyo, Section 1, Problem 46.
I would like to ask, why doesn't Black simply play at instead? Seems dead to me, but now it is 1 am Singapore time, and I might be wrong...
I don't know why I missed this one. At the time I started this page, I was or should have been clearly awake #:-7
What happens if Black plays at in this diagram ?
However, White plays diagonal attachment at and Black has to play to prevent two eyes. Now White throws in at ...
... and she has enough outside liberties to fill in the inside liberty, putting Black in oshitsubushi.