EVENT
BOARDSIZE 19
SETUP W D18 D17 D16 C13 C12 C11 D14 E14 E15 F16 H17 D3 D5 
SETUP B C17 C16 D15 C15 C14 B13 B12 E16 E17 E18 F18 Q16 Q3 
MARK C@K4 A@Q9 B@Q5
COM
Problem 125. Black to play.  

In the upper left corner, Black got profit while White made thickness.
What is the best way for Black to counter this thickness ? 
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B 1 K4
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 reduces the power of White's thickness.
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  VAR
  B 1 Q9
  COM
  Failure.

  Black makes the Chinese-opening formation with 1, but ...
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  W 2 K4
  COM
  ... White gets a chance to take the vital point of 2.
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  B 3 M4
  COM
  If Black now plays 3, ...
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  W 4 L6
  COM
  ... White plays 4 and a huge moyo emerges in the center.
  <=
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  ENDVAR
W 2 Q5
COM
If White approaches with 2, ...
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B 3 R5
W 4 R6
B 5 R4
W 6 Q6
B 7 O4
COM
... Black plays the joseki to 7, taking profit in the lower right.
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W 8 Q10
B 9 Q12
COM
After 9, Black is ahead in territory.
<=
ENDCOM