EVENT
BOARDSIZE 19
SETUP W L17 O17 Q4 S4 O3 K4 D4 D5 D3 E3 E2 H3 C14 C11 
SETUP B C16 D16 J17 Q17 R16 Q10 R6 P6 F3 D2 C2 C3 C4 C6 
MARK \t@L17 \t@O17
COM
Problem 40. Black to play.  

Taking the entire board into account, how should Black attack
the marked stones ? 
ENDCOM
B 1 O15
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is a multi-purpose move. It attacks White's two stones
at the top while expanding Black's moyo on the right.
ENDCOM
  VAR
  B 1 L16
  COM
  Failure.

  Attaching with Black 1 is overly aggressive.
  ENDCOM
  W 2 M16
  B 3 L15
  W 4 K17
  B 5 J16
  W 6 M15
  B 7 M14
  COM
  The sequence to 7 is inevitable.
  ENDCOM
  W 8 O15
  MARK A@L14 B@K16
  COM
  When White jumps to 8, her stones are secure and Black's prospects
  for making a large moyo an the right have been blighted. Moreover,
  Black must worry about the cut of White A or White pushing at
  B.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 K15
  MARK a@L16
  COM
  Failure.

  Although not as bad as Black a, Black 1 here is slack. 
  ENDCOM
  W 2 N15
  MARK B@Q15 A@L15 C@G17
  COM
  White responds by jumping to 2. Black is left without a good
  follow-up, but White has a good move at A (which secures her
  stones) and she is threatening to plaster Black against the left
  side with B. An invasion at C is also an option for her.
  <=
  ENDCOM
  ENDVAR
W 2 L15
COM
White must escape into the center with 2.
ENDCOM
B 3 J15
COM
But Black now jumps to 3, strengthening his position in the upper
left and ...
ENDCOM
W 4 L13
COM
... forcing White to run away with 4.
ENDCOM
B 5 D12
COM
Black has sente, so he attacks the left side with 5 ...
ENDCOM
W 6 C12
B 7 D14
MARK B@N18 A@M16 1@O15
COM
... and 7. Suddenly, a black moyo appears in the upper left.
White's problems are still not over: Black can take more profit
later by peeping at A or making a placement at B. Black 1 follows
the old Chinese go proverb: 'When you want to attack in the west,
make noise in the east.'
<=
ENDCOM