EVENT
BOARDSIZE 19
SETUP W D16 C14 R12 R8 Q4 K4 
SETUP B F17 K16 P17 R16 R10 D4 
MARK \t@R12
COM
Problem 119. Black to play.  

White has invaded with the marked stone. How should Black respond
? 
ENDCOM
B 1 Q11
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Since Black has a strong position at the top. he should attack
the white stone with the diagonal move of 1. Next ...
ENDCOM
  VAR
  B 1 P10
  COM
  Failure.

  Jumping to Black 1 is a slack move.
  ENDCOM
  W 2 S10
  COM
  White can easily make sabaki by attaching underneath with 2.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 P11
  COM
  Failure.

  The knight's move of Black 1 is also slack.
  ENDCOM
  W 2 Q10
  B 3 Q11
  W 4 R11
  B 5 Q9
  W 6 S10
  B 7 P10
  W 8 R9
  COM
  White can link up her stones with the sequence to 8.
  <=
  ENDCOM
  ENDVAR
W 2 R15
COM
White will first play the forcing moves of 2 ...
ENDCOM
B 3 Q16
W 4 S16
COM
... and 4, ...
ENDCOM
B 5 S17
W 6 P13
MARK C@T15 B@T16 A@S14 4@S16 2@R15
COM
... then jump to 6. White 2 and 4 gives White the option of getting
eye shape with a ko by playing the sequence White A - Black B
- White C.
ENDCOM
B 7 O11
W 8 N13
B 9 M11
W 10 L13
B 11 K11
W 12 J13
B 13 H11
W 14 G13
B 15 F11
COM
Black boldly chases White up to 15, 
ENDCOM
W 16 E13
B 17 H16
MARK D@R6
COM
... then defends the top with 17. Black now aims to invade at
D. This result is a great success for Black. White has obtained
no territory, while Black has built a massive wall in the center.
ENDCOM
W 18 M17
MARK \t@H16
COM
After Black defends with the marked stone, invading with White
18 is unreasonable.
ENDCOM
B 19 O14
W 20 O13
B 21 M14
W 22 M13
B 23 K14
MARK 19@O14 21@M14
COM
Black peeps with 19, 21, and 23, ...
ENDCOM
W 24 K13
B 25 L18
COM
... then plays 25, and the territory at the top belongs to Black.
<=
ENDCOM