New reply
I simply changed the "a" and "a" for r and u.
If black is playing, r would be the correct solution, not c.
Playing does not help. White answers with and black cannot play at ``a`` because that would be self atari. So black still needs to play at ``b`` allowing white to win the capturing race with ``c``.
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does not help. White answers with 
and black cannot play at ``a`` because that would be self atari. So black still needs to play at ``b`` allowing white to win the capturing race with ``c``.