EVENT
BOARDSIZE 19
SETUP W J17 N16 O17 N18 P16 L16 
SETUP B D16 G17 P17 Q17 R16 R14 K18 K16 M17 
MARK 3@K16 2@L16 1@K18
COM
Problem 42. White to play.  

How does White respond to Black 3 ? 
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W 1 K17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White should push through with 1 and ...
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  VAR
  W 1 Q15
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  White can avoid complications by first exchanging 1 ...
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  B 2 R15
  COM
  ... for 2 ...
  ENDCOM
  W 3 K17
  COM
  ... before playing 3.
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  B 4 L17
  W 5 L15
  B 6 J18
  W 7 H17
  B 8 H18
  W 9 J15
  MARK A@M16
  COM
  This defends against Black pushing through at A after White 9.
  White gets nice thickness with the joseki to 9.
  <=
  ENDCOM
  ENDVAR
B 2 L17
W 3 M16
B 4 J18
W 5 H17
B 6 H18
W 7 K15
MARK A@J16
COM
... play the moves to 7. This is joseki. Black can still play
A, leading to a complicated fight.
<=
ENDCOM