EVENT
BOARDSIZE 19
SETUP W M17 Q17 R15 C14 D14 C11 
SETUP B D16 C15 F16 K17 
COM
Problem 84. Black to play.  

White's three-space extension from her corner enclosure is ideal.
However, Black has a strong position on the left. How should
Black invade ? 
ENDCOM
B 1 O17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should invade at 1.
ENDCOM
  VAR
  B 1 P17
  COM
  Failure.

  Attaching with 1 ...
  ENDCOM
  W 2 Q16
  B 3 Q18
  W 4 R18
  B 5 N16
  W 6 M16
  B 7 N15
  MARK 5@N16
  COM
  ... and trying to escape with 5 and 7 is not good.
  ENDCOM
  W 8 N17
  MARK 6@M16
  COM
  Black's shape is destroyed when White plays 6 and 8.
  <=
  ENDCOM
  ENDVAR
W 2 M15
COM
If White jumps out with 2, ...
ENDCOM
B 3 O15
COM
... Black escapes into the center with 3.
<=
ENDCOM