EVENT
BOARDSIZE 19
SETUP W D17 F17 G16 E16 C15 E15 C5 R4 O3 O17 N16 P16 O14 P15 
SETUP B C17 D18 E18 E17 F16 D3 E4 R16 Q17 P17 O18 N18 O15 Q14 
COM
Problem 90. Black to play.  

At the top, Black has taken profit while White has gotten influence
in the center. Taking the whole board into consideration, where
is Black's best move ? 
ENDCOM
B 1 P4
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should play 1, breaking the ladder.
ENDCOM
  VAR
  B 1 C8
  COM
  Failure.

  Locally, the pincer of Black 1 is a good point, but ...
  ENDCOM
  W 2 F15
  COM
  ... White will capture with 2 and the aji of the ladder-breaking
  move disappears.
  ENDCOM
  B 3 D6
  COM
  Although Black will become thick with 3 ...
  ENDCOM
  W 4 C6
  B 5 D7
  COM
  ... and 5, White is also thick at the top, so it balances out.
  ENDCOM
  W 6 B3
  MARK 4@C6
  COM
  Moreover, White can live in the corner with 4 and 6.
  <=
  ENDCOM
  ENDVAR
W 2 F15
COM
White has to capture with 2, ...
ENDCOM
B 3 P3
MARK \t@N18
COM
... so Black can then play 3, breaking through White's corner
enclosure. Of course, White becomes thick when she captures,
but the marked black stone serves to diminish the effect of this
thickness.
<=
ENDCOM