EVENT
BOARDSIZE 19
SETUP W M17 R14 Q10 R6 C14 B16 C11 
SETUP B C17 D16 F16 K16 O16 Q16 Q4 O4 K4 D4 
MARK 1@M17
COM
Problem 56. Black to play.  

The deep invasion of 1 is another move White has in her arsenal.
How does  Black reply in this case ? 
ENDCOM
B 1 M16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Attaching with Black 1 is the strongest move. White is now forced
to make life on the side.
ENDCOM
  VAR
  B 1 O17
  COM
  Failure.

  Defending with Black 1 is bad. When White makes a deep invasion,
  your first instinct should be to confine her to the side.
  ENDCOM
  W 2 M15
  COM
  <=
  ENDCOM
    VAR
    W 2 K17
    MARK @@M15
    COM
    Instead of @, White could attach at 2.
    ENDCOM
    B 3 J17
    COM
    Black plays 3 and ...
    ENDCOM
    W 4 J16
    COM
    ... White cuts at 4.
    <=
    ENDCOM
    ENDVAR
  ENDVAR
  VAR
  B 1 N17
  MARK A@L17
  COM
  Failure.

  Attaching with 1 (or A) is even worse.
  ENDCOM
  W 2 M16
  B 3 O14
  W 4 M14
  MARK A@P17
  COM
  White is out into the center and still threatens a move at A.
  <=
  ENDCOM
  ENDVAR
  VAR
  B 1 K17
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  If you are going to defend, Black 1 is the only way.
  ENDCOM
  W 2 M15
  COM
  After White 2, ...
  ENDCOM
  B 3 P13
  COM
  ... Black jumps to 3, attacking White on both the right and the
  left.
  <=
  ENDCOM
  ENDVAR
W 2 N17
B 3 N16
W 4 L17
B 5 K17
W 6 Q18
  VAR
  W 6 L16
  COM
  White could push through with 6 ...
  ENDCOM
  B 7 L15
  W 8 K18
  B 9 J18
  W 10 L19
  B 11 K15
  W 12 P18
  COM
  ... and live with the moves to 12. This is also joseki.
  <=
  ENDCOM
  ENDVAR
B 7 L16
W 8 O17
COM
The moves to 8 are joseki. Black gets territory on the left and
thickness in the center.
<=
ENDCOM