EVENT
BOARDSIZE 19
SETUP W A19 C19 D18 B18 B17 B16 D16 E17 F16 F15 G15 G14 H15 H16 H17 H18 J18 M18 N16 M15 L14 M14 M13 P17 Q17 R18 R16 B11 C11 C12 D12 D13 C10 E10 E9 D6 D4 C4 D3 B3 S3 R4 S5 Q6 G12 H13 H11 H10 H9 K10 
SETUP B R17 S17 S18 Q16 Q15 R13 J17 K18 L18 L17 K16 J15 J14 H14 K13 L13 M12 L11 C18 C17 C16 B15 D15 E14 E13 F13 G13 E12 E11 C14 C13 B13 B12 C3 B2 D2 C2 F3 L3 P4 Q3 R3 G11 G10 G9 G8 
MARK \t@H13 \t@G12 \t@H11 \t@H10 \t@H9 \t@K10
COM
Problem 28. Black to play.  

The marked white stones are floating in the center, but Black's
group in the upper left is also without eyes. What should Black
do ? 
ENDCOM
B 1 G6
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is a calm and solid move which ensures that the black
stones in the upper left are linked to their allies below.
ENDCOM
  VAR
  B 1 H8
  COM
  Failure.

  Black 1 is a forceful move, but it strengthens White's weak group.
  ENDCOM
  W 2 J8
  B 3 J7
  W 4 K8
  B 5 K7
  W 6 L8
  B 7 L7
  W 8 G5
  MARK A@H7 7@L7
  COM
  After 7, White will jump to 8, threatening to cut at A or to
  invade the bottom.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 M9
  COM
  Failure.

  Black 1 is an all-out attack, but ...
  ENDCOM
  W 2 H8
  B 3 G7
  W 4 J6
  B 5 G5
  COM
  ... White will fight like a trapped animal after Black 5. It
  is hard to predict what will happen, but, if White survives,
  Black's territory at the bottom could be wiped out. The sequence
  in the Correct Answer gives Black a sure win.
  <=
  ENDCOM
  ENDVAR
W 2 M9
COM
White's stones must escape into the center. White 2 is reasonable,
but ...
ENDCOM
  VAR
  W 2 H8
  ENDVAR
B 3 O12
COM
... it provokes Black 3.
ENDCOM
W 4 M17
COM
White's group at the top does not have eyes, so she defends with
4.
ENDCOM
B 5 K8
COM
Next, Black goes on to attack with 5 ...
ENDCOM
W 6 L10
B 7 M7
COM
... and 7. The white stones in the center will escape, but Black
has made a huge territory at the bottom.
<=
ENDCOM