EVENT
BOARDSIZE 19
SETUP W D16 E17 D14 F14 G14 G15 K17 K16 L14 O17 P13 P12 Q12 Q5 R4 R3 S2 C4 D4 E4 E3 F4 F5 D10 
SETUP B F16 F17 H16 J16 H14 J14 G13 J12 Q16 Q14 O12 P11 Q10 Q7 R2 Q3 O3 N3 M3 L4 K4 J4 H6 G4 F3 G3 E2 D3 C3 
MARK A@Q12 B@P11 C@P12 D@O12 E@P13
COM
Problem 48. Black to play.  

White has just turned with E. How should Black continue the attack
? 
ENDCOM
B 1 O16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Black 1 leans on the white stone at the top, simultaneously attacking
the three stones below. This move enables Black to get the advantage
either at the top or to put a stone in wait for trapping the
three white stones below.
ENDCOM
W 2 O13
COM
If White turns at 2, ...
ENDCOM
  VAR
  W 2 N16
  COM
  White might resist with 2, ...
  ENDCOM
  B 3 O15
  W 4 O13
  COM
  ... then play 4 ...
  ENDCOM
  B 5 N15
  W 6 N13
  COM
  ... and 6, but ...
  ENDCOM
    VAR
    W 6 N17
    COM
    If White secures the top with 6, ...
    ENDCOM
    B 7 N13
    COM
    ... Black traps the white stones on the right ...
    ENDCOM
    W 8 N12
    B 9 O11
    W 10 N14
    B 11 M13
    W 12 O14
    B 13 M14
    W 14 M15
    B 15 L15
    W 16 M16
    B 17 M12
    COM
    ... with the sequence to 17.
    ENDCOM
    W 18 N11
    COM
    White can't escape with 18 ...
    ENDCOM
    B 19 N10
    COM
    ... because the ladder is unfavourable.
    <=
    ENDCOM
    ENDVAR
  B 7 N17
  COM
  ... Black again secures his position at the top with 7.
  <=
  ENDCOM
  ENDVAR
B 3 N17
COM
... Black quells the white stone at the top with 3. White's stones
in the upper right part of the board are still without a base.
<=
ENDCOM