EVENT
BOARDSIZE 19
SETUP W K16 M17 O16 P17 Q17 
SETUP B D16 H17 M16 Q16 R17 R16 Q14 
MARK \t@Q17 \t@P17
COM
Problem 15. Black to play.  

Having played the marked stones, White returns to attach at 1.
How should Black reply ? 
ENDCOM
B 1 L17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the vital point.
ENDCOM
  VAR
  B 1 N17
  COM
  Unsatisfactory.

  If Black hanes on the other side with 1, ...
  ENDCOM
  W 2 N16
  B 3 L17
  W 4 M18
  B 5 L16
  W 6 L18
  COM
  ... White can make life at the top up to 6 ...
  ENDCOM
  B 7 K17
  COM
  ... in sente.
  <=
  ENDCOM
  ENDVAR
W 2 L16
B 3 N17
W 4 M18
B 5 N16
W 6 N18
B 7 K17
COM
The exchange continues up to 7 and the white stones have become
separated. Moreover, the white group at the top is still not
completely alive.
<=
ENDCOM