EVENT
BOARDSIZE 19
SETUP W C14 D14 D15 D13 J17 J16 J15 R14 Q11 C9 
SETUP B D17 C16 C15 E14 F16 H16 L16 L17 O16 Q16 Q4 K4 D4 
MARK \t@J17 \t@J15 \t@J16
COM
Problem 18. Black to play.  

How should Black attack the three marked stones ? 
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B 1 J13
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black caps with 1.
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  VAR
  B 1 K14
  COM
  Failure.

  The knight's move of Black 1 lacks forcefulness. White ...
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  W 2 J14
  B 3 K13
  W 4 J13
  B 5 K12
  W 6 H11
  COM
  ... runs away with the sequence to 6, and the wall Black makes
  is ineffective because of the two white stones on the right.
  <=
  ENDCOM
  ENDVAR
W 2 G15
COM
If White peeps with 2, ...
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  VAR
  W 2 K14
  COM
  Variation.

  If White tries to escape with 2, ...
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  B 3 L12
  COM
  ... Black keeps her stones confined with the knight's move of
  3.
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  W 4 M14
  COM
  If White 4, 
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  B 5 N12
  MARK A@Q14
  COM
  ... Black 5. If White continues to run away, Black can lean on
  the white stones on the right by attaching at A, so White will
  suffer a loss on the right or lose her stones at the top.
  <=
  ENDCOM
  ENDVAR
B 3 G13
COM
... Black 3 confines the white stones to the top.
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W 4 E17
B 5 E16
W 6 D16
B 7 D18
W 8 C17
B 9 B17
W 10 E18
B 11 C18
W 12 G17
B 13 G16
W 14 H17
B 15 H15
W 16 K18
B 17 L18
W 18 F17
COM
White lives at the top in gote with the sequence to 18, so ...
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B 19 R9
COM
... Black can switch to the right side and attack the two white
stones there with 19.
<=
ENDCOM