EVENT
BOARDSIZE 19
SETUP W D17 C15 D4 D6 Q6 R6 R8 R17 Q17 O17 O18 S10 
SETUP B F3 K4 O4 Q4 R5 Q10 P9 M17 N15 P16 Q16 R16 
MARK A@P9 B@S10
COM
Problem 101. Black to play.  

The diagonal move of Black A looks slack, since it seems as if
White can slide into Black's moyo at the top with B. How should
Black continue ? 
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B 1 S11
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should attach with 1, ...
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W 2 R11
  VAR
  W 2 R10
  MARK 1@S11
  COM
  Variation.

  In answer to Black 1, White might try to secure her stones ...
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  B 3 R11
  W 4 O8
  B 5 P8
  W 6 P7
  COM
  ... with the sequence to 6.
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  B 7 S5
  COM
  But Black secures the corner with 7, while denying White room
  to make two eyes.
  ENDCOM
  W 8 Q11
  COM
  White tries to get some play above with 8 ...
  ENDCOM
  B 9 P11
  W 10 Q12
  B 11 R13
  W 12 Q13
  B 13 R14
  W 14 N10
  COM
  ...to 14, but ...
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  B 15 P12
  W 16 N7
  COM
  ... she must eventually come back and defend with 16 to ensure
  that her stones in the lower right are connected.
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  B 17 M4
  COM
  Black ends the sequence with 17, having secured the territory
  at the bottom and in the upper right. For all of White's intense
  maneuvers, she has only managed to escape with her stones.
  <=
  ENDCOM
  ENDVAR
B 3 S9
COM
... then clamp with 3.
ENDCOM
W 4 S12
MARK 1@S11
COM
White traps the stone at 1, but ...
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B 5 R9
MARK A@R10
COM
... after Black 5 the white stones below and above are under
attack. Note that Black has avoided to play an atari at A because
if White captures this stone she will have an easier time making
a second eye.
<=
ENDCOM