EVENT
BOARDSIZE 19
SETUP W C17 D18 C16 K15 Q17 R15 
SETUP B D17 D16 E18 C15 D14 C10 H16 K17 
MARK 4@E18 3@D18 2@C15 1@C16
COM
Problem 116. White to play.  

After Black 4, White can't live unconditionally. Where does White
play to get a ko ? 
ENDCOM
W 1 B18
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

The only move for White is 1.
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B 2 D19
COM
After Black 2, ...
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  VAR
  B 2 B16
  COM
  Failure.

  If Black 2, ...
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  W 3 B17
  B 4 B15
  W 5 C19
  MARK 3@B17
  COM
  ... White can live unconditionally with 3 and 5.
  <=
  ENDCOM
  ENDVAR
W 3 C19
COM
... White must pin her hopes on a ko by playing 3.
<=
ENDCOM