EVENT
BOARDSIZE 19
SETUP W C15 D16 F17 C12 C8 B6 C5 D4 F4 J3 R8 O17 O18 Q17 R17 S17 
SETUP B C10 D8 B8 B7 C6 D6 L3 P4 R4 R10 Q16 R16 S16 O16 P16 M17 
MARK \t@R8
COM
Problem 42. Black to play.  

How should Black attack the marked stone ? 
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B 1 P9
USER
CORRECT ANSWER
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COM
Correct Answer.

The knight's move of Black 1 is a strong attacking move.
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  VAR
  B 1 R6
  COM
  Failure.

  If Black plays a checking extension to 1, ... 
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  W 2 P8
  MARK A@N3
  COM
  ... White can easily escape into the center with 2. Later, White
  can aim to invade at A.
  <=
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  ENDVAR
W 2 R5
COM
White makes some breathing room for her stones with 2 ...
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B 3 Q5
W 4 R6
COM
... and 4, but ...
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B 5 S4
MARK 3@Q5
COM
... this just induces Black to secure the corner with 3 and 5.
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W 6 P7
COM
When White jumps to 6, ...
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B 7 N8
COM
... Black keeps up the attack with 7, and a moyo in the top right
suddenly appears that extends well into the center. The important
point of this problem is that by attacking a weak white stone,
Black has been able to build his moyo and make his territory
at the bottom secure, while White busily tries to rescue her
stones.
<=
ENDCOM