EVENT
BOARDSIZE 19
SETUP W C12 K17 K15 M17 P18 Q19 R18 R17 Q17 S16 S15 R15 R14 
SETUP B D17 C14 H17 O17 P17 S18 S17 Q15 Q16 R16 O15 
MARK 1@Q19 A@Q18
COM
Problem 109. Black to play.  

White has captured the black stone at A captures with 1. What
should Black do now ? 
ENDCOM
B 1 S19
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should play 1 ...
ENDCOM
  VAR
  B 1 O18
  COM
  Failure.

  Simply playing Black 1 is lukewarm.
  ENDCOM
  W 2 S19
  COM
  White plays 2 and there is no longer any danger to her stones
  in the corner.
  <=
  ENDCOM
  ENDVAR
W 2 R19
  VAR
  W 2 O18
  COM
  If White 2, ...
  ENDCOM
  B 3 R19
  COM
  ... Black plays 3 and White collapses.
  <=
  ENDCOM
  ENDVAR
B 3 O18
COM
... and 3, ...
ENDCOM
W 4 T17
MARK B@N19 A@O19
COM
... then leave the situation as it is. After 4, Black A (or Black
B, threatening ko) could later become double threats against
the white groups on the left and the right.
<=
ENDCOM