EVENT
BOARDSIZE 19
SETUP W K17 Q17 R15 R10 
SETUP B C16 E17 H17 
COM
Problem 78. Black to play.  

White has made wide extensions from her corner enclosure at the
top right. However, White's position is thin  and vulnerable.
Where should Black invade ? 
ENDCOM
B 1 M17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the correct invasion point.
ENDCOM
W 2 K15
  VAR
  W 2 L16
  COM
  Variation.

  White might also attack with 2.
  ENDCOM
  B 3 P17
  COM
  Black would then attach with 3 and, ...
  ENDCOM
    VAR
    B 3 N15
    COM
    If Black 3 here, ...
    ENDCOM
    W 4 O17
    COM
    ... White would attack at 4.
    <=
    ENDCOM
    ENDVAR
  W 4 Q16
  B 5 Q18
  COM
  ... after 5, ...
  ENDCOM
  W 6 R18
  B 7 N15
  COM
  ... jump to 7.
  <=
  ENDCOM
  ENDVAR
B 3 M15
W 4 K13
MARK 2@K15
COM
If White jumps to 2 and 4, ...
ENDCOM
B 5 M13
MARK 3@M15
COM
... Black follows her into the center with 3 and 5.
<=
ENDCOM