EVENT
BOARDSIZE 19
SETUP W D16 D10 D6 D4 K17 O17 Q12 P13 P4 P3 Q3 P2 R4 S4 R3 
SETUP B Q16 Q14 Q10 O12 F3 K4 Q4 P5 Q5 R5 S5 O4 O3 O2 N6 
MARK A@O12 B@P13
COM
Problem 105. Black to play.  

Black A is not seen very often, but it is a valid move. How should
Black continue after White B ? 
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B 1 O16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 directly attacks the stone at the top and, from a distance,
the two stones below.
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W 2 N16
B 3 O15
W 4 P17
B 5 Q17
COM
After the sequence to Black 5, ...
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W 6 O13
COM
... White pushes into the center with 6.
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B 7 N17
COM
Black now plays 7 ...
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W 8 M17
  VAR
  W 8 M13
  MARK @@M17
  COM
  Variation.

  Instead of @ in the Correct Answer, if White jumps to 8 here,
  ...
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  B 9 M16
  W 10 N15
  B 11 N14
  W 12 M15
  B 13 N13
  COM
  ... Black could play the sequence to 13 and trap the white stones
  on the right side.
  <=
  ENDCOM
  ENDVAR
  VAR
  W 8 N13
  COM
  Variation.

  If White 8 here, ...
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  B 9 M17
  COM
  ... Black secures the top with 9.
  <=
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  ENDVAR
B 9 N18
COM
... and 9.
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W 10 M18
COM
After White 10, ...
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B 11 M16
COM
... Black cuts with 11, ...
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W 12 N15
B 13 N14
COM
... then ataris with 13.
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W 14 M15
B 15 N13
COM
After Black 15, the three white stones on the right side are
trapped. This leaning attack is similar to the one in Problem
48.
<=
ENDCOM