EVENT
BOARDSIZE 19
SETUP W D16 D4 K4 Q14 R14 Q11 
SETUP B Q3 Q9 K16 O16 Q16 R15 
MARK 1@Q11
COM
Problem 87. Black to play.  

This time White defends with the extension of 1 on the fourth
line. How should Black respond ? 
ENDCOM
B 1 N4
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is a flexible move. It defends against a white approach
move.
<=
ENDCOM
  VAR
  B 1 O9
  COM
  Failure.

  If Black jumps to 1, ...
  ENDCOM
  W 2 O11
  COM
  ... White will also jump to 2. It is better for Black to defer
  this defence until later because, since White's stone on the
  upper right is high, she has no good way to invade on the side.
  <=
  ENDCOM
  ENDVAR