EVENT
BOARDSIZE 19
SETUP W D16 D14 D3 N16 O16 P16 Q17 R16 S16 
SETUP B Q3 F17 K16 M17 N17 O17 R15 Q15 Q13 
MARK A@R9 B@R6 C@Q5
COM
Problem 119. Black to play.  

How should Black play on the right side: at A, B, or C ? 
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B 1 R9
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Since it is a good idea to strengthen your weak stones, Black
plays 1, the ideal move to defend his three stones in the upper
right. It also works well with his stone below.
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  VAR
  B 1 Q5
  COM
  Failure.

  If Black encloses the corner with 1, ...
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  W 2 Q10
  COM
  ... White pincers with 2.
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  B 3 R8
  COM
  Black 3 is a good move, but ...
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  W 4 P9
  COM
  ... White 4 prevents the black stones above from linking up with
  their allies below. They must flee, so White gets the initiative.
  <=
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  ENDVAR
W 2 C5
B 3 K3
W 4 H3
B 5 C12
COM
The game continues to Black 5.
<=
ENDCOM