EVENT
BOARDSIZE 19
SETUP W C17 C16 D15 D13 C12 F17 H17 G15 H15 J15 K15 K16 H13 J12 N16 P16 Q17 R16 S16 S17 P17 
SETUP B C18 D17 E18 E16 E15 E14 G14 F12 D4 Q4 Q16 J16 J17 K17 L16 L15 K14 L13 M15 M14 R17 Q15 D9 R18 R15 
MARK A@S17 B@R18 C@P17 D@R15 E@S16
COM
Problem 50. Black to play.  

After the sequence to White E, how should Black attack the white
stones at the top center ? 
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B 1 J10
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black must cap at 1.
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W 2 H11
COM
If White 2, ...
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  VAR
  W 2 H10
  COM
  Variation.

  Attaching with 2 is White's best chance to create complications,
  but ...
  ENDCOM
  B 3 H11
  W 4 J11
  B 5 H12
  W 6 J13
  B 7 J9
    VAR
    B 7 L11
    COM
    Jumping to Black 7 is also a strong move.
    ENDCOM
    W 8 G13
    B 9 E11
    W 10 K10
    B 11 J9
    W 12 K11
    B 13 P15
    COM
    Here too, Black exchanges 13 ...
    ENDCOM
    W 14 S18
    COM
    ... for 14, ...
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    B 15 M10
    MARK 1@J10
    COM
    ... then starts to map out his moyo with 15, while keeping the
    white stones under attack. See Problem 135 for another response
    to the cap of Black 1.
    <=
    ENDCOM
    ENDVAR
  W 8 G13
  B 9 E11
  COM
  ... Black secures his stones with 9. White must escape.
  ENDCOM
  W 10 L12
  COM
  If she attaches with 10, ...
  ENDCOM
  B 11 P15
  COM
  ... Black plays the sente move of 11 ...
  ENDCOM
  W 12 S18
  B 13 M12
  COM
  ... and attacks with 13 ...
  ENDCOM
  W 14 L11
  B 15 N10
  COM
  ... and 15 Black will build a moyo while White escapes.
  <=
  ENDCOM
  ENDVAR
B 3 G12
MARK A@J13
COM
... Black 3 threatens to cut off the white stones at the top
with A, ...
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W 4 J13
COM
... so White must defend there.
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B 5 G9
COM
Black 5 now blocks White's escape route.
<=
ENDCOM