EVENT
BOARDSIZE 19
SETUP W C15 D16 F16 J17 M17 R14 R11 
SETUP B O17 O15 R16 C14 D14 D11 
COM
Problem 118. White to play.  

Black's position at the top is vulnerable. Where should White
invade ? 
ENDCOM
W 1 R17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White 1 is the vital point.
ENDCOM
B 2 Q16
COM
If Black 2, ...
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  VAR
  B 2 Q17
  COM
  Variation.

  If Black blocks with 2, ...
  ENDCOM
  W 3 S17
  B 4 S16
  W 5 Q18
  MARK A@Q16 3@S17
  COM
  ... White will play 3 and 5. Since White has the cutting point
  of A, she can live.
  <=
  ENDCOM
  ENDVAR
W 3 S16
B 4 S15
W 5 S17
B 6 R15
W 7 P18
COM
... White lives with the moves to 7.
<=
ENDCOM