EVENT
BOARDSIZE 19
SETUP W E17 D17 C16 C14 C13 R17 P17 S15 R4 Q3 O4 P6 P7 Q6 R6 S6 Q8 O8 N8 N7 M10 
SETUP B D14 D13 D12 E16 F17 G16 N17 O15 Q15 E4 K4 Q5 R5 S7 R7 Q7 P8 P9 Q9 O9 O7 
COM
Problem 73. Black to play.  

All of White's groups are safe. What should Black do ? 
ENDCOM
B 1 L13
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Since there is nothing to attack, now is a good time for Black
to reinforce his moyo at the top with 1. Black can expect a large
territory here.
<=
ENDCOM
  VAR
  B 1 N9
  COM
  Failure.

  In the game, Black cut trough with 1 ...
  ENDCOM
  W 2 M9
  B 3 M8
  COM
  ... and 3, hoping to isolate the white stones in the center and
  attack them.
  ENDCOM
  W 4 L8
  B 5 M7
  W 6 N6
  B 7 L7
  COM
  But the black stones became heavy and vulnerable.
  <=
  ENDCOM
  ENDVAR