EVENT
BOARDSIZE 19
SETUP W D17 F17 H17 E3 D9 D12 
SETUP B D15 F15 H15 K15 Q16 Q4 
MARK A@K17 B@Q10 D@L4 C@C4
COM
Problem 143. Black to play.  

In the upper left, Black has invested a lot of stones to attack
White, but his four stones there aren't taking any territory
and he seems to be falling behind. Where should he play to rectify
the balance of territory ? 
ENDCOM
B 1 Q10
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should make a sanren-sei on the right with 1, aiming to
make a moyo.
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  VAR
  B 1 K17
  COM
  Failure.

  The scale of Black 1 is too small. Also, it is not a serious
  threat against the white group, so ...
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  W 2 R11
  COM
  ... White plays on the right with 2, preventing Black from making
  a large-scale moyo.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 L4
  COM
  Failure.

  If Black 1 here, ...
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  W 2 R10
  COM
  ... White will play 2.
  <=
  ENDCOM
  ENDVAR
W 2 O3
COM
In the game, Black answered the approach move at 2 ...
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B 3 P5
COM
... with the diagonal move at 3.
<=
ENDCOM