EVENT
BOARDSIZE 19
SETUP W D16 D13 C6 D4 K4 O5 O3 O2 P15 
SETUP B P3 Q4 Q6 O7 R10 R16 P17 O16 J16 F17 
MARK 2@O16 1@P15
COM
Problem 156. White to play.  

When Black considers the top important, he will play 2. In that
case, White will focus her attention on the right. Try to think
a few moves ahead and give White a shape that is not heavy. 
ENDCOM
W 1 Q16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White must first play 1, ...
ENDCOM
  VAR
  W 1 R15
  MARK @@Q16
  COM
  Failure.

  If you immediately attach with 1, neglecting to first play at
  @, ...
  ENDCOM
  B 2 Q16
  COM
  ... Black will play 2 himself, ...
  ENDCOM
  W 3 Q15
  B 4 N14
  COM
  ... then jump out into the center with 4. White's three stones
  are heavy and almost without hope.
  <=
  ENDCOM
  ENDVAR
B 2 Q17
W 3 R15
COM
... then 3.
ENDCOM
B 4 S16
W 5 Q11
  VAR
  W 5 R12
  COM
  Failure.

  White 5 is heavy.
  ENDCOM
  B 6 P11
  MARK \t@S16
  COM
  Black launches an attach with 2 and this stone, in concert with
  the marked stone, will make it hard for White to get sabaki.
  <=
  ENDCOM
  ENDVAR
B 6 R11
W 7 Q12
B 8 Q10
W 9 O11
B 10 P10
W 11 N14
MARK A@R3
COM
Up to 11, White makes a fine sabaki. Black has solidified his
lower right side, but there still remains a white invasion at
A.
<=
ENDCOM