EVENT
BOARDSIZE 19
SETUP W C17 D17 E17 G17 H17 J17 P17 P10 P8 Q6 Q5 Q4 P3 O4 E3 J4 C11 E11 G11 
SETUP B C15 F15 E16 H16 J16 K16 M16 P16 Q17 R16 Q3 R3 R4 R5 R7 R8 C4 D5 C9 E9 
COM
Problem 168. White to play.  

This is another after-the-fuseki problem. Where is the vital
point for White to play ? 
ENDCOM
W 1 H9
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

The knight's move of White 1 is the vital point. With this move,
White builds a moyo in the center and Black is now unable to
use his thick wall above to attack White.
ENDCOM
  VAR
  W 1 G9
  MARK @@H9
  COM
  Failure.

  There is a big difference between White 1 and the knight's move
  at @ in the Correct Answer.
  ENDCOM
  B 2 F10
  MARK \t@C9
  COM
  The double peep of Black 2, anchored by his marked stone, is
  now a strong move.
  ENDCOM
  W 3 E14
  B 4 D16
  W 5 H12
  MARK 3@E14
  COM
  After White 3 and 5, ...
  ENDCOM
  B 6 G10
  COM
  ... Black can cut through with Black 6 ...
  ENDCOM
  W 7 H10
  B 8 H9
  COM
  ... and Black 8.
  <=
  ENDCOM
  ENDVAR
  VAR
  W 1 F9
  COM
  Failure.

  Attaching with 1 only helps Black ...
  ENDCOM
  B 2 F8
  W 3 G9
  B 4 G8
  W 5 H9
  B 6 H8
  COM
  ... to march into White's potential moyo with the sequence to
  6.
  <=
  ENDCOM
  ENDVAR
  VAR
  W 1 F5
  COM
  Failure.

  Although White 1 is often a good move, in this case it is too
  small in scale.
  ENDCOM
  B 2 G9
  W 3 J11
  B 4 J9
  W 5 L11
  B 6 L9
  COM
  Black advances into White's sphere of influence with the sequence
  to 6 while using his thickness to maintain the pressure on White.
  <=
  ENDCOM
  ENDVAR
B 2 F10
COM
If Black peeps at 2, ...
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W 3 E14
COM
... White defends by forcing with 3, ...
ENDCOM
B 4 D16
W 5 H12
COM
... then playing the diagonal move of 5.
<=
ENDCOM