Go Problem of the Week

In addition to Aikido, I've been trying to improve my Go game...with that in mind, I am going to try to go through a different Go problem every week here. And for the first one...

What should black do to capture the marked white stones?



Once Black 1 is played below, the two marked white stones are as good as captured. If White 2 was played at Black 3, Black could have played at A, and ultimately capture even more of White's stones.