EVENT
BOARDSIZE 19
SETUP W D17 G17 H17 J17 L17 L16 M15 M14 M13 N16 R6 Q4 P3 C4 C5 C7 C8 D10 D11 L12 K12 K5 
SETUP B Q16 Q9 O3 O2 O5 D3 D4 D5 D7 E9 C15 F15 H16 J16 K16 J14 L15 L14 L13 M12 M11 H4 
MARK \t@K12 \t@L12 A@K5
COM
Problem 93. Black to play.  

White, seemingly unable to decide how to play with his marked
stones, makes a probe with A. How should Black attack ? 
ENDCOM
B 1 K7
MARK A@R3 \t@K5
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black should cap the marked stone with 1. This move isolates
the two stones above. Although Black may not be able to capture
this stone, he will be able to reinforce his position before
going after the two stones above. In addition, he is aiming at
the invasion of A.
ENDCOM
  VAR
  B 1 K3
  MARK \t@K5
  COM
  Failure.

  Answering the marked stone with Black 1 is submissive.
  ENDCOM
  W 2 H5
  COM
  White will force with 2, ...
  ENDCOM
  B 3 G4
  W 4 K9
  COM
  ... then jump to 4. White should now have no trouble making
  two eyes within Black's sphere of influence.
  <=
  ENDCOM
  ENDVAR
W 2 K3
COM
If White jumps down to 2, ...
ENDCOM
B 3 L4
COM
... Black will peep at 2.
ENDCOM
W 4 K4
COM
Connecting at 4 is bad, because the three white stones are dead
...
ENDCOM
  VAR
  W 4 L5
  COM
  White answered Black's peep with 3. This was a resourceful answer.
  ENDCOM
  B 5 K4
  W 6 J4
  B 7 J5
  W 8 J3
  B 9 L3
  W 10 H5
  B 11 J6
  W 12 G4
  COM
  White was able to make sabaki with the sequence to 12. Next ...
  ENDCOM
  B 13 G7
  COM
  Black 13 is a calm move.
  ENDCOM
    VAR
    B 13 F3
    COM
    Failure.

    After White 12, it is not a good idea to deprive White of a base
    with Black 13.
    ENDCOM
    W 14 G3
    B 15 G5
    W 16 H6
    B 17 H7
    W 18 G6
    B 19 F5
    W 20 L2
    B 21 M2
    W 22 F6
    B 23 F4
    W 24 F8
    MARK B@R3 A@N4
    COM
    The sequence continues to 23, and White has escaped. Next, the
    peep of White A will be troublesome for Black, and takes away
    the value of an invasion at B.
    <=
    ENDCOM
    ENDVAR
  W 14 F3
  COM
  White must play at 14 to live, ...
  ENDCOM
  B 15 F11
  MARK A@R3
  COM
  ... but Black 15 surrounds a vast framework of territory. Next,
  Black can aim to invade the lower right corner at A. Black has
  a won game.
  <=
  ENDCOM
  ENDVAR
B 5 H3
MARK A@R3
COM
... after Black 5. Black still aims at A.
ENDCOM