EVENT
BOARDSIZE 19
SETUP W B17 C17 D17 E16 E15 C14 C13 D11 D4 Q5 Q7 R6 R11 
SETUP B B18 D18 E18 E17 B16 C16 D16 C15 Q3 O3 R4 R5 R16 P17 
COM
Problem 66. White to play.  

There is a wide space between White's thickness on the upper
left and her stone below. However, Black has a good attacking
move on the upper right. What should White do ? 
ENDCOM
W 1 D6
MARK A@R14
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White might be tempted to extend to A on the right side, but,
in this case, it is better to strengthen the stone in the lower
left with 1.
ENDCOM
  VAR
  W 1 R14
  COM
  Failure.

  If White extends to 1, ...
  ENDCOM
  B 2 C6
  COM
  ... Black approaches at 2 and breaks up White's position on the
  left side ...
  ENDCOM
  W 3 C5
  B 4 D6
  W 5 F4
  B 6 C9
  COM
  ... with the sequence to 6. The effectiveness of White's thickness
  above is now neutralised.
  <=
  ENDCOM
  ENDVAR
B 2 R13
COM
If Black 2, ...
ENDCOM
W 3 N4
COM
... White will play 3 ...
ENDCOM
B 4 O4
W 5 N6
MARK B@R8
COM
... and 5, mapping out a large-scale moyo. Note that White 5
indirectly defends against the invasion at B.
<=
ENDCOM