EVENT
BOARDSIZE 19
SETUP W D18 E17 F16 F15 D16 D15 D14 E14 D13 C5 Q4 
SETUP B C18 B17 D17 C17 C16 C15 D3 E4 R10 Q16 
COM
Problem 111. Black to play.  

White has a very thick position at the top left. Black wants
to counter this thickness. What is the best move for him to do
this ? 
ENDCOM
B 1 N17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

The large knight's move of black 1 is the ideal extension. In
does not approach White's thickness too closely, yet it does
not allow White to make a full extension from it.
ENDCOM
  VAR
  B 1 K17
  COM
  Failure.

  Black 1 is too near to White's thickness.
  ENDCOM
  W 2 M17
  COM
  White will take the initiative by invading at 2.
  ENDCOM
  B 3 K15
  W 4 M15
  B 5 K13
  W 6 M13
  MARK 2@M17 4@M15
  COM
  White now gets influence facing the right with the stones at
  2, 4, and 6.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 L17
  COM
  Failure.

  If Black 1 here, ...
  ENDCOM
  W 2 N17
  COM
  ... White will invade at 2.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 M17
  COM
  A bit dangerous.

  Black 1 is also a bit thin because ...
  ENDCOM
  W 2 O17
  COM
  ... White can invade at 2.
  ENDCOM
  B 3 O16
  COM
  If Black next attaches at 3, ...
  ENDCOM
  W 4 P16
  COM
  ... White 4 is a good counterattack.
  <=
  ENDCOM
  ENDVAR
W 2 L17
COM
White 2 is as far as White can extend, but ...
ENDCOM
B 3 L16
COM
... Black will attach with 3.
ENDCOM
W 4 K16
B 5 L15
W 6 M17
B 7 N16
MARK 4@K16 2@L17 6@M17
COM
White's stones at 2, 4, and 6 do not fully utilise her thickness,
so they are not working efficiently.
<=
ENDCOM