EVENT
BOARDSIZE 19
SETUP W C17 C3 R6 R9 
SETUP B C10 Q3 R4 R16 P17 
MARK 1@R16 2@C17 9@C10 4@C3 6@R6 8@R9 5@P17 3@Q3 7@R4
COM
Problem 72. White to play.  

In this opening, all the corners have been occupied and Black
has taken a big point with 9. Where should White play next ?
ENDCOM
W 1 R12
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White 1 is the only move.
ENDCOM
  VAR
  W 1 K3
  COM
  Failure.

  If White plays here, ...
  ENDCOM
  B 2 R11
  COM
  ... Black 2 would be a severe attack against the white stones.
  Black 2 is also an ideal extension from his corner enclosure
  above.
  <=
  ENDCOM
  ENDVAR
B 2 K3
MARK A@C5 B@C15
COM
Black 2, Black A, or Black B all have the same value.
<=
ENDCOM