mithra wrote:
Maybe offtopic, but is B B3 really a ko threat?
After W tenuki, B B4, W C5, B A2, W A3, B has nothing.
What do I miss?
Good catch!

It threatens only one point. D-01 becomes a Black sente instead of gote.
In the real game White would have done better to ignore it and fill the ko, for White +9. More evidence that White misread the position.
Edit: In the variation, if White ignores it and fills the ko, the result is White +7 instead of White +9. It makes a 2 point difference because Black has not made the second approach move yet. (The approach moves are inside White territory.) I am adding these variations to #15. Many thanks, mithra!
