EVENT
BOARDSIZE 19
SETUP W D16 G17 D10 C6 D4 Q5 Q6 R6 R10 P10 
SETUP B C14 F3 K4 P4 Q3 R4 R5 R12 R16 P16 L17 
MARK \t@C14
COM
Problem 88. White to play.  

Black has entered White's sphere of influence with the marked
stone. How should White respond ? 
ENDCOM
W 1 C16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

White 1 not only secures the corner, it also attacks the black
stone.
ENDCOM
  VAR
  W 1 C15
  COM
  Failure.

  Attacking with 1 ...
  ENDCOM
  B 2 D14
  W 3 D12
  COM
  ... and 3 is also possible.
  ENDCOM
  B 4 F14
  COM
  If Black jumps to 4, ...
  ENDCOM
    VAR
    B 4 C12
    MARK 3@D12
    COM
    Black makes sabaki.

    After White 3, Black can attach with 4 ...
    ENDCOM
    W 5 C11
    B 6 E12
    COM
    ... and 6, ...
    ENDCOM
    W 7 E11
    B 8 D13
    COM
    ... then atari with 8.
    ENDCOM
    W 9 D11
    COM
    If White connects with 9, ...
    ENDCOM
    B 10 F12
    COM
    ... Black can extend to 10. Black has a more resilient shape
    than in the Correct Answer, so this result is not as good for
    White.
    <=
    ENDCOM
    ENDVAR
  W 5 B15
  MARK 4@F14
  COM
  ... White secures the corner with 5. This result is also good
  for White. But Black will not play 4.
  <=
  ENDCOM
  ENDVAR
B 2 C12
COM
If Black extends to 2, ...
ENDCOM
  VAR
  B 2 E14
  MARK 1@C16
  COM
  Variation.

  If Black responds to White 1 by jumping to 2, ...
  ENDCOM
  W 3 D13
  COM
  ... White will peep with 3, ...
  ENDCOM
  B 4 D14
  W 5 G15
  COM
  ... then jump to 5. Black's stones are still under attack and
  an invasion into White's corner in the upper left is no longer
  possible.
  <=
  ENDCOM
  ENDVAR
W 3 C10
COM
... White makes an iron pillar with 3. Black's stones are still
under attack.
<=
ENDCOM