EVENT
BOARDSIZE 19
SETUP W D18 E18 G17 H17 D17 D15 C15 R14 P14 N14 R11 P2 O2 O3 N4 K4 J4 H3 F5 D11 F7 D6 C4 D3 E3 
SETUP B E17 E16 E15 G16 H16 J16 P17 R16 R9 P9 P11 Q6 Q4 Q2 P3 H4 G4 F4 F3 E4 H6 H8 F9 D9 
MARK \t@N14 \t@P14 \t@R14 \t@R11
COM
Problem 55. Black to play.  

How should Black attack the four marked stones in the upper right
? 
ENDCOM
B 1 Q13
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer

Black should peep with 1, ...
ENDCOM
W 2 Q14
B 3 S12
COM
... then make a placement at 3.
ENDCOM
W 4 P16
COM
White can no longer make two eyes on the right side, so she has
to switch to the top and ...
ENDCOM
  VAR
  W 4 S15
  COM
  Variation.

  The placement of Black 3 is a flexible move. For example, if
  White exchanges 4 ...
  ENDCOM
  B 5 S16
  COM
  ... for 5, ...
  ENDCOM
  W 6 R12
  B 7 S11
  MARK A@R13 6@R12
  COM
  ... Black can crawl to 7 if White plays 6. Since White has to
  defend her defect at A, Black will end in sente.
  <=
  ENDCOM
  ENDVAR
B 5 Q17
W 6 O17
B 7 O18
W 8 N17
B 9 N18
W 10 M17
COM
... play the sequence to 10, inducing Black to secure the corner.
ENDCOM
B 11 F11
COM
Black ends in sente, so he takes the key point of 11 to reach
out to his stones above and to start building a moyo in the center.
<=
ENDCOM
  VAR
  B 11 O6
  COM
  Failure.

  The aim of 11 here is to map out a moyo with ...
  ENDCOM
  W 12 F11
  B 13 M5
  COM
  ... 13 and ...
  ENDCOM
  W 14 M4
  B 15 K6
  COM
  ... 15, but ...
  ENDCOM
  W 16 G9
  COM
  ... White attaches at 16 and a sharp exchange ensues.
  ENDCOM
  B 17 G10
  W 18 G8
  B 19 F10
  W 20 H9
  COM
  White turns at 20 and Black's moyo becomes thin.
  <=
  ENDCOM
    VAR
    W 20 G12
    COM
    ... White could also play 20 here attacking Black's stones at
    the top. 
    ENDCOM
    B 21 H9
    COM
    Black would respond at 21.
    <=
    ENDCOM
    ENDVAR
  ENDVAR