EVENT
BOARDSIZE 19
SETUP W D17 C14 G3 K3 R5 R10 P17 
SETUP B C4 E4 P4 Q3 R12 Q15 R16 
MARK 1@G3
COM
Problem 41. Black to play.  

White makes a two-space extension with 1. What should Black do
now ? 
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B 1 R8
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should take this opportunity to invade White's thin position
on the side with 1.
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W 2 P10
COM
If White jumps to 2, ...
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  VAR
  W 2 P5
  COM
  Variation.

  White could also attach with 2.
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  B 3 O5
  COM
  Black will hane with 3, ...
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  W 4 P6
  B 5 P8
  MARK B@O3 A@O4
  COM
  ... then jump to 5. The cut at A might look worrisome, but Black
  can secure his stones at the bottom by playing an atari at B.
  (See Problem 17 in Get Strong at Invading.)
  <=
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  ENDVAR
B 3 Q6
COM
... Black will play 3, and the lone white stone on the lower
right side is in trouble.
<=
ENDCOM