xela: and are a standard combination to undermine the eye at 'a'.
unkx80: You may want to consider this variation.
xela: White continues this way? White 'a' next, and black can't escape... but it looks messy. Is there a better way?
(If throws in at the marked stone, then at makes a seki.)
Yohei: looks ok, but the , exchange is bad timing.
Black needs to answer at (or at a, but this makes very little difference), and now white can exchange for .
xela: On second thoughts, this looks better. Black can't play 'a'.
blackman: Black can play this way too.