EVENT
BOARDSIZE 19
SETUP W F17 K16 O17 
SETUP B D16 D14 Q16 Q14 
COM
Problem 26. Black to play.  

White's position is impressive but it is yet no territory. Where
should Black invade ? 
ENDCOM
B 1 M17
MARK A@H17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black invades with 1. Since the position is symmetrical, he could
just as well have invaded at A.
ENDCOM
  VAR
  B 1 H17
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  Also correct.
  <=
  ENDCOM
  ENDVAR
W 2 N16
B 3 H17
W 4 G16
MARK 2@N16
COM
If White responds with the diagonal moves at 2 and 4, ...
ENDCOM
B 5 K17
COM
... Black attaches at 5. Black is firmly established at the top.
<=
ENDCOM