(;
GM[1]
SZ[19]
AW[dd][fc][dj][dp][kq][ko][kl]
AB[jd][pd][pf][qk][mm][np][pq]
LB[fp:A][fq:B][er:C]
TR[kl]
C[Problem 123. Black to play.  

White has just played the marked stone, mapping out a huge moyo on the left, so the lower left is now the most important place to play. But where should Black play: at A, B, or C ? ]
(;B[fp]
TE[2]
C[Correct Answer.  

Black should approach high with 1. ]
;W[dn]
C[If White 2, ... ]
;B[ip]
LB[km:A]
C[... Black extends to 3, aiming to exploit the thinness of White's two-space jump by attaching at A. ]
;W[jn]
C[White will defend at 4, but ... ]
;B[hn]
C[... Black plays 5, wiping out much of White's moyo. <= ]
)
(;B[fq]
C[Failure.  

White answers Black 1 ... ]
;W[fo]
C[... by capping at 2. ]
;B[cq]
C[If Black invades the corner with 3, ... ]
;W[dq];B[cp];W[co];B[bo];W[cn];B[bn];W[cm];B[dr];W[er];B[cr];W[eq]
TR[kl]
C[... after the sequence to 14, the marked stone makes a huge moyo with White's other stones on the left. <= ]
)
(;B[er]
C[Failure.  

If Black 1 here, ... ]
;W[fq]
C[... White makes a bigger moyo with 1. <= ]
)
)