EVENT
BOARDSIZE 19
SETUP W D16 C14 C11 C4 D3 G3 Q5 Q6 R6 R10 P17 Q14 
SETUP B C9 C6 E6 O3 Q3 R4 R5 R16 R13 R14 F17 J16 M17 
COM
Problem 158. White to play.  

White's two stones in the upper right are floating without a
base. How should White strengthen them ? 
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W 1 R17
MARK \t@R14 \t@Q14
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Since White exchanged the marked stones before attaching at 1,
...
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  VAR
  W 1 D18
  MARK A@K3
  COM
  Failure.

  Territorially, White 1 and White A are big moves, but ...
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  B 2 R17
  MARK 1@D18
  COM
  ... Black will descend at 2 and the two white stones are left
  floating in the center without a base. Before any other move,
White 1 at 2 is absolutely essential.
  <=
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  ENDVAR
B 2 S17
COM
... Black is now forced to follow the joseki with 2 ...
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W 3 Q16
B 4 R15
COM
... and 4.
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W 5 R18
COM
After descending to 5, White has made a base for her stones.
All her groups are now safe.
<=
ENDCOM