EVENT
BOARDSIZE 19
SETUP W B18 C18 D18 D17 E16 F17 D12 C8 C2 D3 E3 G3 K3 R10 
SETUP B C17 B17 A16 B15 C15 D15 D16 D14 E17 B3 C3 D4 C5 F5 P3 R4 Q16 
MARK A@O17 B@R14 C@R7
COM
Supplement to Problem 120: White's best move.

Instead of A and C in the Problem Diagram, ...
ENDCOM
W 1 B13
USER
CORRECT ANSWER
ENDUSER
COM
... White should have played 1. This move threatens the eye shape
of the black stones above, so if Black invades on the left side,
the fighting could spill over the top and the black stones there
could get into trouble. For that reason, White 1 is a good move
because it reinforces her thin stones on the left.
<=
ENDCOM