EVENT
BOARDSIZE 19
SETUP W J17 L16 M17 O17 
SETUP B D16 G17 L17 M16 Q17 Q16 R13 
MARK 4@M17 3@M16 2@L16 1@L17
COM
Problem 23. Black to play.  

Against Black's invasion, White attaches at 2 and cuts with 4.
How should Black respond ? 
ENDCOM
B 1 K16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black is strong on the right, so Black 1 ...
ENDCOM
  VAR
  B 1 N17
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  Black 1 ...
  ENDCOM
  W 2 M18
  B 3 M15
  COM
  ... and 3 are a nice tesuji.
  ENDCOM
  W 4 N18
  B 5 K16
  W 6 L18
  B 7 L15
  COM
  Black gets a nice ponnuki in the center of the board with the
  moves to 7.
  <=
  ENDCOM
  ENDVAR
W 2 L15
B 3 K17
COM
... and 3 are best. White's position on the right still has defects,
but Black is strong on both sides.
<=
ENDCOM