EVENT
BOARDSIZE 19
SETUP W D16 D14 C11 C5 D4 F4 Q5 Q6 R6 Q10 Q11 R12 R13 Q13 R14 
SETUP B C9 C6 D6 O3 Q3 R4 R5 R16 Q15 Q14 P13 P12 Q12 F17 L17 
MARK A@L15 B@G14 C@E9
COM
Problem 136. Black to play.  

In this position, White has profit while Black has a moyo at
the top. However, the black stones on the lower side are not
very strong. How should Black continue ? 
ENDCOM
B 1 L15
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should strengthen his position at the top with 1.
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  VAR
  B 1 E9
  COM
  Failure.

  Black strengthens his position with 1 and prepares to attack
  the top and bottom.
  ENDCOM
  W 2 L15
  COM
  But White wipes out Black's moyo with the sequence from 2 ...
  ENDCOM
  B 3 J16
  W 4 O14
  B 5 P14
  W 6 M17
  COM
  ... to 6.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 G14
  COM
  Failure.

  If Black 1 here, White could easily invade this moyo.
  <=
  ENDCOM
  ENDVAR
W 2 E10
COM
White attacks with 2, but ...
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B 3 F6
COM
... Black simply jumps to 3 and, ...
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W 4 H4
COM
... after White 4, ...
ENDCOM
B 5 L3
COM
... Black 5 is a big extension, aiming to slide under White's
position on the left.
<=
ENDCOM