EVENT
BOARDSIZE 19
SETUP W D16 G17 D10 C6 D4 Q5 Q6 R6 R10 P10 
SETUP B C17 F3 K4 P4 Q3 R4 R5 R12 R16 P16 L17 
MARK \t@C17
COM
Problem 97. White to play.  

Black invades the corner with the marked stone. How should White
respond ? 
ENDCOM
W 1 C16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White should block at 1 and build a moyo in the upper left.
ENDCOM
B 2 D17
W 3 E17
B 4 E18
W 5 F18
B 6 E16
COM
After Black exchanges 6 ...
ENDCOM
W 7 F17
COM
... for 7, ...
ENDCOM
B 8 B16
W 9 B15
B 10 B17
W 11 C14
B 12 D18
COM
... Black lives in the corner with the sequence to 12, but ...
ENDCOM
  VAR
  B 12 E15
  MARK @@D18
  COM
  Variation.

  Instead of @ in the preceding diagram, Black might first extend
  to 12 ...
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  W 13 D14
  B 14 D18
  COM
  ... before connection at 14.
  ENDCOM
  W 15 F14
  COM
  Next, White traps the two black stones with 15.
  <=
  ENDCOM
  ENDVAR
W 13 E15
MARK A@N17
COM
... White gets a thick position after playing 13. Since she is
thick on the left side, White can now aim to invade at A.
<=
ENDCOM