EVENT
BOARDSIZE 19
SETUP W D16 D10 D4 Q14 N16 O17 P17 R18 
SETUP B K4 K16 Q16 Q15 O16 O15 Q10 Q4 
COM
Problem 30. Black to play.  

Black has made a sanren-sei on the right side and occupied both
star points in the middle of the upper and lower sides. What
is Black's best move in this position ? 
ENDCOM
B 1 N15
MARK \t@K16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should push along the fifth line, forcing White in the direction
of the marked stone. All of Black's stones are now working together
harmoniously.
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  VAR
  B 1 O4
  COM
  Failure.

  If Black plays somewhere else, such as at 1, ...
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  W 2 N15
  COM
  ... White will seize the initiative at the top with 2 ...
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  B 3 P13
  W 4 G16
  MARK \t@K16
  COM
  ... and 4. The marked black stone is now under a severe attack.
  <=
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  ENDVAR
W 2 M16
COM
If White 2, ...
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B 3 M15
COM
... Black continues to press White with 3.
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W 4 O3
COM
If White next approaches with 4, ...
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B 5 O5
MARK C@L16 B@N18 A@M18
COM
... Black 5 builds a magnificent moyo on the right side . Moreover,
Black still threatens White with the sequence Black A - White
B - Black C.
<=
ENDCOM