EVENT
BOARDSIZE 19
SETUP W D16 O17 L17 P9 R9 S5 K3 C3 D4 F4 
SETUP B Q16 Q17 R11 P11 Q5 Q3 M3 B4 C6 C9 
MARK \t@S5
COM
Problem 9. Black to play.  

White has just slid under Black's corner enclosure with the marked
stone. How should Black attack White's position on the right
? 
ENDCOM
B 1 R6
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 and ...
ENDCOM
  VAR
  B 1 S3
  COM
  Failure.

  Black 1 lets White ...
  ENDCOM
  W 2 R7
  COM
  ... settle her group with 2. White now has nothing to worry about.
  ENDCOM
  ENDVAR
  VAR
  B 1 R4
  COM
  Failure.

  Black 1 here is also bad.
  ENDCOM
  W 2 R7
  COM
  White responds with 2.
  <=
  ENDCOM
  ENDVAR
W 2 S6
B 3 S7
COM
... 3 stop White from making eyeshape.
ENDCOM
  VAR
  B 3 R7
  MARK @@S7
  COM
  Failure.

  The hane @ in the Correct Answer is the key move. It is a mistake
  for Black to extend to 3.
  ENDCOM
  W 4 S7
  B 5 R8
  W 6 S8
  B 7 S9
  W 8 S10
  B 9 Q9
  W 10 R10
  B 11 Q10
  W 12 S11
  COM
  White can live with the sequence to 12 and Black's moyo in the
  upper right has been erased.
  <=
  ENDCOM
  ENDVAR
W 4 S8
  VAR
  W 4 R7
  MARK \t@S7
  COM
  Variation.

  When Black blocks with the marked stone, White might cut with
  4. But ... 
  ENDCOM
  B 5 R8
  W 6 Q7
  B 7 S9
  W 8 Q8
  B 9 S8
  COM
  ... Black can link up to his allies above with the sequence to
  9. White is now split into two weak groups.
  <=
  ENDCOM
  ENDVAR
B 5 R7
W 6 T7
MARK A@S3 B@Q9 4@S8
COM
White links up with 4 and 6, but even if she jumps to A, she
doesn't have two eyes yet. Black is also threatening to wedge
in with B.
<=
ENDCOM