EVENT
BOARDSIZE 19
SETUP W C14 D16 K17 S12 S11 R11 R10 S9 T9 T8 S7 Q7 O6 R6 Q5 S5 T4 J3 D4 F4 C3 
SETUP B P17 R16 R13 S13 R12 S10 R9 R8 S8 Q11 Q10 P8 R5 R4 S4 S2 Q3 O3 B4 C6 C9 
COM
Problem 159. Black to play.  

The fuseki has ended and the middle game has begun. Black has
made a thick wall on the right. What is the best way for him
to utilise this wall ? 
ENDCOM
B 1 H17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Invading at 1 is the best way for Black to use his thickness.
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  VAR
  B 1 M17
  COM
  Failure.

  Thickness should be used to attack. If Black tries to make territory
  with 1 ...
  ENDCOM
  W 2 K15
  B 3 M15
  COM
  ... and 3, ...
  ENDCOM
  W 4 E17
  MARK 2@K15
  COM
  ... White takes the lead with 2 and 4. The black stones on the
  right are now overconcentrated, while White's stones are taking
  territory efficiently.
  <=
  ENDCOM
  ENDVAR
W 2 K15
COM
If White 2 ...
ENDCOM
B 3 H15
W 4 K13
COM
... and 4, ...
ENDCOM
B 5 H13
MARK 3@H15
COM
... Black keeps up the pressure with 3 and 5.
ENDCOM
W 6 N17
COM
White makes a base for her stones with 6, but ...
ENDCOM
B 7 D18
COM
... Black slides to 7 and White is behind in territory.
<=
ENDCOM