EVENT
BOARDSIZE 19
SETUP W P16 R17 P3 Q3 R4 R6 D4 C10 
SETUP B C16 E16 K17 R16 P4 O3 O4 C6 J3 
MARK D@L3 C@C5 B@C8 A@C13 \t@C6
COM
Problem 144. White to play.  

Black has played the marked stone, separating the white stones
on the left. Black has strong positions above and below, so attacking
this stone in not a good idea. Where should White play ? 
ENDCOM
W 1 C13
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White should extend to 1, strengthening her weakest stone.
ENDCOM
  VAR
  W 1 C5
  COM
  Failure.

  If White defends her corner with 1 ...
  ENDCOM
  B 2 D6
  W 3 F3
  COM
  ... and 3, the white stone on the side will come under attack
  ...
  ENDCOM
  B 4 C12
  COM
  ... when Black extends from his corner enclosure with 4.
  ENDCOM
  W 5 E10
  B 6 F6
  COM
  After 6, Black has taken the lead.
  <=
  ENDCOM
  ENDVAR
B 2 F3
COM
Next, Black will approach with 2 and ...
ENDCOM
W 3 F4
COM
... White responds by attaching with 3.
ENDCOM
B 4 G4
W 5 E3
B 6 F5
W 7 E4
COM
After White 7, all of White's stones are secure.
<=
ENDCOM