(;
GM[1]
SZ[19]
AW[dd][jd][nc][po][qn][ol][dp]
AB[pd][pf][pk][pq][qp][qo][jp]
LB[ol:1][pn:A]
C[Problem 51. Black to play.  

White 1 is a light move. You might think that the cutting point at A is a serious weakness in White's position, but Black must not cut there. What should he do instead ? ]
(;B[ok]
TE[2]
C[Correct Answer.  

Black 1 ... ]
;W[nl];B[nk]
C[... and 3 are the most natural moves. ]
;W[ml]
C[After White 4, ... ]
;B[lj]
C[... Black jumps to 5 and a black moyo on the right side emerges. Moreover, White's stones are still not settled. <= ]
)
(;B[pn]
C[Failure.  

It is tempting to cut at 1, but this falls into a trap. ]
;W[on]
C[White forces ... ]
;B[pm];W[pl];B[qm];W[ql]
C[... with the sequence to 6 and Black's potential territory and moyo on the upper right suddenly disappears. <= ]
)
)