EVENT
BOARDSIZE 19
SETUP W C12 K17 M17 Q17 Q16 R15 R14 
SETUP B D17 C14 H17 O17 Q18 Q15 
MARK 2@Q16 1@Q18
COM
Problem 91. Black to play.  

What does Black do if White answers 1with 2 ? 
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B 1 R18
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Wrenching the corner territory away from White with 1 is the
natural move.
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  VAR
  B 1 P18
  COM
  Failure.

If Black draws back with 1, ...
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  W 2 R18
  COM
  ... White takes the corner with 2 and Black's shape has been
  destroyed.
  <=
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  ENDVAR
W 2 O16
COM
Next, White attaches with 2.
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B 3 P17
W 4 P16
B 5 S16
COM
Black's invasion is a success.
<=
ENDCOM