This move, making nice shape (see OkiWantsIkkenTobi), captures and simultaneously protects against the placement at a. Any other move would allow Black either to capture two stones or to place a stone at a, connect it and reduce White to one eye.
All in all, this is a familiar line of play. Black can't connect at because of shortage of liberties
Because of the circled liberty, White can descend to , because Black's play at a is not atari.
Hmmm. This variation is probably even not worth giving. Anyway, it is important for White to answer at
.
at first this also seems to work, but the switch at is a wrecking move.
Problem 35
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