EVENT
BOARDSIZE 19
SETUP W M17 R17 R16 R14 S14 Q4 D4 B16 C14 C11 
SETUP B D16 C17 F16 K16 Q17 Q16 Q15 P13 R12 K3 
MARK \t@M17
COM
 Black to play.  

White has invaded deep inside Black's moyo with his marked stone.
What should Black do ? 
ENDCOM
B 1 K17
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is a solid move. It secures Black's territory in the
top left and prevents White from establishing a base there.
ENDCOM
  VAR
  B 1 M15
  COM
  Failure.

  If Black caps with 1, ...
  ENDCOM
  W 2 K17
  COM
  ... White can make a base for her stones at the top by attaching
  with 2.
  ENDCOM
  B 3 J17
  W 4 L16
  B 5 L15
  W 6 J16
  COM
  After the exchange of White 6 ...
  ENDCOM
  B 7 K15
  COM
  ... for Black 7, ...
  ENDCOM
  W 8 J18
  B 9 H17
  W 10 H18
  B 11 G17
  W 12 L18
  B 13 N18
  W 14 G18
  B 15 F18
  W 16 K19
  MARK \t@C11 \t@C14 \t@B16
  COM
  ... White can easily live with the sequence to 16. Compared to
  the Correct Answer, Black has failed to get any territory at
  the top and, with White's marked stones on the left, his thickness
  is ineffective.
  <=
  ENDCOM
  ENDVAR
W 2 M15
COM
White is forced to escape into the center, but ...
ENDCOM
B 3 N16
COM
... Black peeps with 3, ...
ENDCOM
W 4 M16
B 5 M13
COM
... then severely attacks by capping with 5.
ENDCOM
W 6 L14
B 7 K12
MARK 6@L14
COM
In response to White 6 Black exchanges 7 ...
ENDCOM
W 8 J14
COM
... for White 8, ...
ENDCOM
B 9 D12
COM
... then switches to the left and forces with 9.
ENDCOM
W 10 C12
B 11 H12
W 12 G14
B 13 H15
W 14 H14
COM
After the sequence to White 14, ...
ENDCOM
B 15 D14
COM
... Black attaches with 15 and the white stones are in trouble.
<=
ENDCOM