EVENT
BOARDSIZE 19
SETUP W K17 O17 O16 
SETUP B D16 H17 P17 Q16 Q14 
COM
Problem 25. Black to play.  

White has made an ideal extension from her two stones on the
right. However, it is still possible to invade this position.
Where does  Black play ? 
ENDCOM
B 1 M17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should invade at 1.
ENDCOM
W 2 M16
COM
If White attaches at 2, ...
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  VAR
  W 2 M18
  COM
  Variation.

  If White attached underneath with 2, ...
  ENDCOM
  B 3 N18
  W 4 N17
  B 5 L18
  W 6 M16
  B 7 L17
  W 8 L16
    VAR
    W 8 O18
    COM
    If White 8 here, ...
    ENDCOM
    B 9 L16
    COM
    ... Black plays 9. Either way, Black is satisfied.
    <=
    ENDCOM
    ENDVAR
  B 9 O18
  COM
  ... Black would play the moves to 9.
  <=
  ENDCOM
  ENDVAR
B 3 L17
W 4 L16
B 5 K18
MARK 3@L17
COM
... Black links up to his allies on the left with 3 and 5.
<=
ENDCOM