GokyoShumyoSection4Problem7/Attempts
LukeNine45: Did I miss anything?
erislover: Another variation to consider is white at .
MrTenuki Hmmm, at ...
This would lead to a ko with black taking first. But black has a better move.
can't be played at a or b due to a shortage of liberties. So white has no choice but to approach from the top, and black wins the capturing race.