EVENT
BOARDSIZE 19
SETUP W C17 D10 D4 F3 K16 O17 
SETUP B Q16 Q14 Q9 Q5 Q3 K4 
COM
Problem 151. Black to play.  

The black and white moyos divide the board. With one move, however,
Black can break up White's moyo and wipe out much of it's influence.
ENDCOM
B 1 D16
MARK B@C16 A@D17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Making a large-scale moyo from the 3-3 point is unnatural because
Black will land a devastating blow in the center of White's position
with 1. White will respond with A or B.
ENDCOM
  VAR
  B 1 E17
  COM
  Black is under attack.

  Playing one line deeper with 1 is bad ...
  ENDCOM
  W 2 D15
  COM
  ... because Black will come under a severe attack with 2 ...
  ENDCOM
  B 3 H17
  W 4 K17
  COM
  ... and 4.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 E16
  COM
  Failure.

  If Black 1 here, ...
  ENDCOM
  W 2 D15
  COM
  ... White 2 is again the vital point.
  <=
  ENDCOM
  ENDVAR
W 2 C16
B 3 D15
W 4 E18
B 5 C15
COM
After the moves to 5, Black's stones are quite resilient and
cannot be easily attacked.
ENDCOM
W 6 F16
COM
If White 6, ...
ENDCOM
B 7 F15
COM
... Black attaches at 7.
<=
ENDCOM