(;
GM[1]
SZ[19]
AW[cc][dd][ce][de][df][fc][kd][og][oi][qi][pn][qn][qo][qp][pp][qq][pr][qs][rr][dq][do][ck][cg]
AB[hc][ie][oc][qd][qg][pl][nl][rm][pq][oq][or][op][oo][po][on][ip][ci][bd][cf][dg][eg][ef]
TR[kd]
C[Problem 56. Black to play.  

How should Black attack the marked white stone at the top ? ]
(;B[nf]
TR[kd]

TE[2]
C[Correct Answer.  

Black 1 aims at both the marked stone and the three white stones on the right side. ]
(;W[ng]
C[If White defends with 2, ... ]
;B[kf]
TR[kd]
C[... Black caps with 3 and the marked stone is trapped. <= ]
)
(;W[kf]
LB[nf:1]
C[Variation.  

In answer to Black 1, White might escape into the center with 2, but ... ]
;B[mh]
TR[qi][oi][og]
C[... the three marked stones are in trouble after Black 3. <= ]
))
(;B[kf]
C[Failure.  

If Black immediately caps with 1, ... ]
;W[nd]
C[... White makes a shoulder hit at the vital point of 2. ]
;B[od];W[ne]
C[After 4, White's stones form a cohesive and resilient group, having a lot of room to maneuver. It will be hard for Black to find an effective attack against them. <= ]
)
(;B[md]
C[Failure.  

Black 1 is completely unconvincing. ]
;W[kf]
C[White jumps down into the center with 2, and Black doesn't have a good follow-up. <= ]
)
)