(;
GM[1]
SZ[19]
AW[dd][jd][nc][dp][mo][po]
AB[pd][pf][pk][jp][pq][qp]
LB[mo:1]
C[Problem 43. Black to play.  

White 1 is a good move because it is light and aims to make sabaki. Black, however, must not play passively. Instead, he must pursue White persistently. Where should he play ? ]
(;B[op]
TE[2]
C[Correct Answer.  

Before anything else, Black must play 1, ... ]
;W[nn];B[mq]
C[... then take territory at the bottom with 3. ]
;W[nk]
C[After White caps at 4, this skirmish will come to a pause, but Black still has attacking chances. <= ]
)
(;B[qo]
C[Failure for Black.  

If Black crawls at 1, ... ]
;W[mq]
TR[jp]
C[... White will jump into the bottom with 2, separating the marked stone from its allies on the right. This stone could come under attack later on. <= ]
)
)