EVENT
BOARDSIZE 19
SETUP W D16 D13 C6 D4 K4 O5 O3 O2 P15 
SETUP B P3 Q4 Q6 O7 R10 P17 R16 Q15 J16 F17 
MARK 2@Q15 1@P15
COM
Problem 158. White to play.  

The attachment of Black 2 is a move used in special situations.
It is a move contrary to the go principle of not attaching against
attacking stones. But in this case, Black's corner is strong
and he is not worried about eyes. Try to read five moves ahead.
ENDCOM
W 1 P16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

By bumping against Black with 1, White is looking for a way to
make shape.
ENDCOM
B 2 O17
COM
Black 2 is absolutely necessary.
ENDCOM
W 3 Q14
COM
After that, White 3 ...
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B 4 Q16
W 5 O13
COM
... and 5 make good shape.
<=
ENDCOM
  VAR
  W 5 P13
  COM
  Failure.

  White 5 here would create a heavy shape.
  <=
  ENDCOM
  ENDVAR