EVENT
BOARDSIZE 19
SETUP W D17 C4 
SETUP B Q4 Q16 
MARK 1@Q16 2@D17 4@C4 3@Q4
COM
Problem 37. Black to play.  

When White makes this komoku formation on the left side with
2 and 4, from which side should Black approach ? 
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B 1 E4
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

The high approach of Black 1 in the lower left corner works best
with Black's niren-sei formation on the right.
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W 2 E3
B 3 F3
W 4 D3
B 5 F4
  VAR
  B 5 G4
  COM
  Variation.

  In this game, White answered Black 5 ...
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  W 6 D6
  COM
  ... with 6, so ...
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  B 7 Q10
  COM
  ... Black switched to the right side, making a sanren-sei with
  7.
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  W 8 O3
  COM
  White then approaches with 8, but ...
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  B 9 M3
  COM
  ... Black 9 became an ideal move, being both a pincer and an
  extension from his stones on the left.
  <=
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  ENDVAR
W 6 C6
COM
If the joseki to White 6 is played, ...
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B 7 K4
MARK B@Q10 A@D15
COM
... Black makes an ideal extension to 7 at the bottom. A corner
enclosure at White A would now seem natural, but Black would
make a sanren-sei with B, so ...
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W 8 R6
COM
... White plays 8 to prevent this.
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B 9 R8
W 10 R3
B 11 Q3
W 12 R4
B 13 Q5
W 14 S6
B 15 P7
COM
Still, Black gets a moyo at the bottom when he plays 15.
<=
ENDCOM