EVENT
BOARDSIZE 19
SETUP W D16 C17 F17 D4 C6 R3 S2 P3 P2 O2 R6 Q6 R9 
SETUP B B16 C14 C11 F3 K4 N2 O3 O4 Q4 P4 R5 S5 R11 Q16 
MARK \t@R9 \t@Q6 \t@R6
COM
Problem 31. Black to play.  

How can Black use his thickness to attack the marked white stones
? 
ENDCOM
B 1 P10
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

The knight's moves of Black 1 ..
ENDCOM
  VAR
  B 1 P9
  COM
  Failure.

  Capping at 1 is ineffective because Black is not using his thickness
  below.
  ENDCOM
  W 2 Q10
  COM
  White breaks through Black's position with 2, and Black is left
  without a good follow-up move.
  <=
  ENDCOM
  ENDVAR
W 2 P8
B 3 N9
MARK a@L16
COM
... and 3 are severe. White's stones can live, but Black will
have built up influence in the center. He can then stake out
a moyo by extending to A.
<=
ENDCOM