EVENT
BOARDSIZE 19
SETUP W C17 K15 Q17 R15 
SETUP B D17 D16 D14 C10 H16 K17 
MARK 1@D17
COM
Problem 107. White to play.  

Against White's invasion, Black blocks with 1. How does White
respond ? 
ENDCOM
W 1 B16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White 1 is the Correct Answer.
ENDCOM
  VAR
  W 1 C16
  COM
  Failure.

  White 1 is a bad move.
  ENDCOM
  B 2 C15
  COM
  Black blocks with 2 and, ...
  ENDCOM
  W 3 D18
  B 4 E18
  W 5 C18
  B 6 B16
  COM
  ... after 6, White has no room to make two eyes.
  <=
  ENDCOM
  ENDVAR
B 2 B14
COM
Black confines White to the corner with 2, ...
ENDCOM
W 3 D18
B 4 E18
W 5 B18
B 6 D19
W 7 C18
COM
... but White lives up to 7.
<=
ENDCOM