EVENT
BOARDSIZE 19
SETUP W D16 D4 L3 O3 R10 O17 N16 N14 
SETUP B C10 Q4 Q6 Q16 Q14 P17 L17 L15 
MARK \t@N14
COM
Problem 10. Black to play.  

White has just jumped out into the center with the marked stone.
How should Black play ? 
ENDCOM
B 1 Q11
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 is the key point. It keeps the white stones at the top
separated from their ally on the right side.
ENDCOM
  VAR
  B 1 M13
  COM
  Failure.

  In some positions ...
  ENDCOM
  W 2 N13
  B 3 M12
  W 4 N12
  B 5 M11
  COM
  ... a wall with the sequence to 5 can be good strategy, but ...
  ENDCOM
  W 6 O10
  COM
  ... here these moves enable White to link up her stones and isolate
  Black's stones in the upper right. Although they are strong enough
  to live, White will be able to make profit by threatening them.
  <=
  ENDCOM
  ENDVAR
W 2 Q10
COM
White first exchanges 2 for ...
ENDCOM
  VAR
  W 2 M13
  MARK @@Q10
  COM
  Variation.

  Instead of @ in the Correct Answer, White might immediately play
  the diagonal move of 2.
  ENDCOM
  B 3 K13
  COM
  Black could first exchange 3 for ...
  ENDCOM
  W 4 M11
  COM
  ... 4, then ...
  ENDCOM
  B 5 Q10
  MARK \t@R10
  COM
  ... quell the marked white stone with 5. Although this stone
  has some aji, Black can look forward to some profit on the right
  side.
  <=
  ENDCOM
  ENDVAR
B 3 P11
COM
... 3, then ...
ENDCOM
W 4 M13
COM
... returns to take care of her stones at the top by moving out
with 4.
ENDCOM
B 5 K13
COM
Black attacks with 5, then ...
ENDCOM
W 6 M11
B 7 P10
COM
... plays another move against White's stones on the right. It
is hard to predict how this fight will continue, but the white
stones on the right are being severely pressed and if White tries
to save then, it could spill over and affect the five white stones
at the top.
<=
ENDCOM