EVENT
BOARDSIZE 19
SETUP W D16 K17 S11 R10 Q10 Q11 O11 P9 D4 F3 J3 K3 L3 N3 N4 
SETUP B Q16 Q13 O13 R12 Q9 R9 R7 Q3 P4 N5 O5 M4 L4 K4 H5 
MARK \t@H5 \t@K4 \t@L4 \t@M4 \t@N5 \t@O5 \t@O11 \t@P9 \t@Q10 \t@Q11
MARK \t@R10 \t@S11
COM
Problem 77. Black to play.  

Note the thick black wall (the marked stones) at the bottom.
How should Black attack the marked white ones ? 
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B 1 M12
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black drives White into his thick wall at the bottom with the
knight's moves of 1 ...
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  VAR
  B 1 M11
  COM
  Failure.

  The cap of Black 1 drives the white stones in the wrong direction.
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  W 2 N12
  B 3 L13
  W 4 N13
  COM
  After 4, White's stones should have no trouble making two eyes.
  <=
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  ENDVAR
W 2 M10
B 3 K11
COM
... and 3.
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W 4 P8
B 5 Q7
W 6 K9
COM
After 6, White can probably live, but Black gets influence in
the center, giving him a huge advantage at the top.
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B 7 H17
COM
Black now uses his advantage by invading at 7.
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W 8 K15
B 9 H15
W 10 N17
COM
White extends to 10, but ...
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B 11 O18
COM
... Black plays the vital point of 11, ...
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W 12 K13
B 13 J14
COM
... then confines the white stones at the top with 13 ...
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W 14 K14
B 15 J12
MARK A@D14
COM
... and 15. White will live in gote, but, in the process, Black
will be able to strengthen his corner. With this sente, Black
will next play A.
<=
ENDCOM