EVENT
BOARDSIZE 19
SETUP W D16 C14 L17 R17 R16 R14 S14 L3 D4 C3 F3 
SETUP B F17 J16 Q17 Q16 Q15 P13 R12 Q4 B4 C6 C9 
MARK \t@L17
COM
Problem 57. Black to play.  

White has just invaded with the marked stone. How should Black
respond ? 
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B 1 K17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Denying your opponent's stones a base makes attacking easy. Black
1 here ...
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  VAR
  B 1 L15
  COM
  Failure.

  The cap of Black 1 is ineffective.
  ENDCOM
  W 2 J18
  COM
  White slides to 2 and ...
  ENDCOM
  B 3 H17
  W 4 H18
  B 5 G18
  W 6 G16
  B 7 G17
  W 8 N17
  COM
  ... easily lives at the top with the sequence to 8.
  <=
  ENDCOM
  ENDVAR
W 2 L15
COM
... forces White to escape with 2, so ...
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  VAR
  W 2 L16
  COM
  Variation.

  White 2 leaves the white stones heavy. With Black's wall on the
  right, White has no room to develop her stones.
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  B 3 K14
  COM
  The knight's move of Black 3 is now a strong attack.
  ENDCOM
  W 4 L14
  B 5 L13
  W 6 M14
  MARK A@M13
  COM
  White 6 at A is also possible. For this variation, see Problem
  133.
  ENDCOM
  B 7 M13
  W 8 O15
  B 9 Q14
  W 10 N13
  B 11 N12
  W 12 O13
  B 13 O12
  W 14 O17
  B 15 P18
  MARK B@M4 A@R18
  COM
After the sequence to Black 15, the white stones on the top are
  under attack and Black is threatening the white corner with a
  hane at A, In addition, Black has made a wall on the outside
  from which he can now map out a huge moyo with a shoulder hit
  at B.
  <=
  ENDCOM
  ENDVAR
B 3 K14
COM
... Black can continue the chase with 3.
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W 4 O15
COM
White 4 ...
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B 5 Q14
COM
... forces Black to defend with 5, but, ...
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W 6 M13
COM
... after White 6, ...
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B 7 M11
COM
... Black caps with 7 and White's stones are under siege. See
Problem 134 for the continuation.
<=
ENDCOM