xela: White can't play a without first connecting at all of b, c and d--so black is effectively ahead six liberties to five.
xela: Note that the throw-in at is important...
If , then creates an eye. White still needs to fill all of a, b, c, and d, to put Black in atari, so Black is still ahead in the capturing race.
Bass is silly, b could have taken the cutting stones by playing at b :-)