EVENT
BOARDSIZE 19
SETUP W K17 M18 O17 
SETUP B D16 H17 M17 Q16 Q14 
MARK 1@M18
COM
Problem 13. Black to play.  

White attaches with 1. What should Black do ? 
ENDCOM
B 1 N18
MARK B@K4 A@L18
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

There are two Correct Answers: Black 1 and A.

Black might even play elsewhere (B).
<=
ENDCOM
  VAR
  B 1 L18
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  Also correct.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 K4
  W 2 M16
  COM
  Variation.

  If Black played elsewhere, White might then attach from above
  with 2.
  ENDCOM
  B 3 P17
  COM
  Black forces with 3 ...
  ENDCOM
  W 4 O16
  B 5 O18
  COM
  ... and 5, ...
  ENDCOM
  W 6 N18
  COM
  ... then takes sente again.
  <=
  ENDCOM
    VAR
    W 6 N18
    ENDVAR
  ENDVAR