EVENT
BOARDSIZE 19
SETUP W D17 C15 C4 Q5 R6 Q7 R11 
SETUP B E3 Q3 O3 R4 R5 R13 R16 P17 
MARK 1@R13 A@R8
COM
Problem 80. White to play.  

Black has just played 1, threatening to invade at A. How should
White respond ? 
ENDCOM
W 1 K17
MARK A@P11
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Locally, White A is the proper move, but, taking the whole board
into account, White should extend from her corner enclosure to
1.
ENDCOM
  VAR
  W 1 P11
  MARK \t@R13
  COM
  Failure.

  White 1 is the proper move, but this makes the marked stone a
  forcing move and ...
  ENDCOM
  B 2 J17
  COM
  ... Black can take the big point of 2.
  ENDCOM
  W 3 P13
  COM
  If White 3, ...
  ENDCOM
    VAR
    W 3 G17
    COM
    If White 3 here, ...
    ENDCOM
    B 4 P13
    COM
    ... Black jumps to 4.
    <=
    ENDCOM
    ENDVAR
  B 4 F17
  COM
  ... Black extends to 4.
  <=
  ENDCOM
  ENDVAR
B 2 R8
COM
Even if Black invades at 2, ...
ENDCOM
W 3 S7
COM
... White can fight and get a reasonable result.
ENDCOM
B 4 Q10
COM
If Black then goes for thickness with the sequence from 4 ...
ENDCOM
  VAR
  B 4 S10
  MARK @@Q10
  COM
  Variation.

  Instead of 4 at @, Black could go for territory with 4 ...
  ENDCOM
  W 5 Q9
  B 6 Q10
  COM
  ... and 6 here.
  ENDCOM
  W 7 R10
  B 8 R9
  W 9 P9
  B 10 S11
  W 11 P4
  B 12 P3
  W 13 R12
  B 14 S12
  W 15 P11
  COM
  However, White settles her stones and gets thickness with the
  sequence to 15. (See Get Strong at Invading, Problems 27, 30,
  33, 36, 39, and 42 for other versions of this joseki.)
  <=
  ENDCOM
  ENDVAR
W 5 R10
B 6 R9
W 7 S9
B 8 S8
W 9 T8
B 10 S10
W 11 T9
B 12 Q11
W 13 S11
B 14 R12
W 15 S12
B 16 S13
COM
... to 16, White's group is safe and ...
ENDCOM
W 17 P8
MARK \t@K17
COM
... the marked white stone and 17 neutralise Black's thickness.
<=
ENDCOM