EVENT
BOARDSIZE 19
SETUP W D16 Q3 N3 Q8 P12 R17 Q16 R18 P17 P15 O15 
SETUP B C4 E3 O5 R5 O16 O13 P14 Q14 R15 R16 S17 
COM
Problem 154. Black to play.  

A sharp encounter has taken place in the upper right. Black's
stones are out in the center and he would like to play a big
extension on the left. Should Black so this immediately or should
he make another move on the right ? 
ENDCOM
B 1 R12
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the most urgent point. This move makes Black's stones
in the upper right absolutely safe and it also takes away space
for White to make her own stones safe.
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  VAR
  B 1 R3
  COM
  Failure.

  If Black makes a base for his stones in the lower right with
  1, ...
  ENDCOM
  W 2 R2
  COM
  ... White will exchange 2 ...
  ENDCOM
  B 3 S3
  COM
  ... for 3, ...
  ENDCOM
  W 4 R12
  COM
  ... then secure her stones on the right side with 4. The black
  stones above are still insecure and the game now favours White.
  <=
  ENDCOM
  ENDVAR
W 2 O8
COM
If White jumps to 2, ...
ENDCOM
  VAR
  W 2 R11
  COM
  If White 2 here, ...
  ENDCOM
  B 3 S11
  COM
  ... Black will play 3.
  <=
  ENDCOM
  ENDVAR
B 3 P4
COM
... Black forces with 3, ...
ENDCOM
W 4 P3
B 5 M5
COM
... then jumps to 5. White is still under attack.
<=
ENDCOM