EVENT
BOARDSIZE 19
SETUP W D16 K4 K6 K8 C4 C6 D3 E3 
SETUP B Q16 Q10 Q4 M4 E4 F4 F3 F7 
MARK 2@D16 1@Q16 11@Q10 3@Q4 13@M4 12@K4 14@K6 16@K8 4@C4 6@E3
MARK 8@D3 10@C6 15@F7 5@E4 9@F4 7@F3
COM
Problem 17. Black to play.  

This problem is a bit different from Problem 13. After 167, Black's
four stones on the left seem to be in trouble. How can Black
relieve the pressure on these stones and go on the attack ? 
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B 1 D7
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should first play the forcing moves of 1 ...
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  VAR
  B 1 K16
  COM
  Failure.

  If Black neglects to strengthen his stones on the left and plays
  a big point at 1 instead, ...
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  W 2 E6
  COM
  ... White will force with 2 ...
  ENDCOM
  B 3 F6
  W 4 G5
  COM
  ... and 4, ...
  ENDCOM
  B 5 F5
  W 6 F9
  COM
  ... then cap with 6. Black's stones are now in trouble.
  <=
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  ENDVAR
W 2 C7
B 3 D8
COM
... and 3, strengthening his stones on the left, ...
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W 4 C9
B 5 K10
COM
... then cap with 5. It is now the three white stones in the
middle of the lower side that are under attack, caught between
the sanren-sei formation on the right and Black's strengthened
position on the left.
<=
ENDCOM