EVENT
BOARDSIZE 19
SETUP W K17 Q17 R14 C12 
SETUP B D17 C14 H17 
COM
Problem 73. Black to play.  

Where should Black invade White's position on the right ? 
ENDCOM
B 1 O17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 aims at White's enclosure on the right.
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  VAR
  B 1 M17
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  Black 1 is also a vital point.
  ENDCOM
  W 2 O17
  COM
  White will answer with 2 and ...
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  B 3 L16
  COM
  ... Black attacks the white stone on the left with 3.
  <=
  ENDCOM
  ENDVAR
W 2 Q15
COM
If White defends with 2, ...
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B 3 M17
W 4 K15
B 5 N14
COM
... the moves to 5 are the normal development.
<=
ENDCOM