EVENT
BOARDSIZE 19
SETUP W C12 K17 M17 Q17 R18 R15 R14 
SETUP B D17 C14 H17 O17 Q18 Q15 
MARK 2@R18 1@Q18
COM
Problem 94. Black to play.  

White answers Black 1 by blocking at 2. What should Black do
? 
ENDCOM
B 1 Q16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the vital point.
<=
ENDCOM
  VAR
  B 1 P17
  MARK @@Q16
  COM
  Failure.

  Of course, Black would like to play at 1, but he cannot do so
  unless he has played @ in the Correct Answer.
  ENDCOM
  W 2 Q16
  COM
  Now White takes the point 2, and Black's shape has collapsed.
  <=
  ENDCOM
  ENDVAR