EVENT
BOARDSIZE 19
SETUP W K17 P16 R16 
SETUP B D17 D15 H17 R13 R10 
COM
Problem 108. Black to play.  

Where should Black attack White's moyo at the top ? 
ENDCOM
B 1 M17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the vital point.
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W 2 L16
COM
If White 2, ...
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  VAR
  W 2 O17
  COM
  Variation.

  If White defends the corner with 2, ...
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  B 3 L16
  COM
  ... Black will play 3, and the lone stone on the left will come
  under attack.
  <=
  ENDCOM
  ENDVAR
B 3 O17
COM
... Black forces with 3, ...
ENDCOM
W 4 P17
B 5 N15
COM
... then jumps to 5. Black has made light sabaki.
<=
ENDCOM