(;
GM[1]
SZ[19]
AW[dd][df][dj][dp][jp][qf][pk][ok][nk][nj][ql]
AB[pq][fc][jd][pd][re][qh][qj][qk][oj][oi][mh]
C[Problem 170. Black to play.  

Black's moyo in the upper right has almost turned into sure territory. However, his stone in the lower right corner seems to have gotten left behind in the battle above. Black must not forsake this stone, but what is the best way to strengthen it ? ]
(;B[mp]
TE[2]
C[Correct Answer.  

Because White is thick above, Black should extend tightly with the large knight's move of 1. Black's stones at the bottom are now safe. <= ]
)
(;B[lp]
C[Dubious.  

Extending all the way to 1 leaves Black a bit thin. ]
;W[jn]
LB[np:A]
C[White will jump to 2, and Black will be troubled by the possibility of a white invasion at A. ]
;B[ln]
C[If Black jumps to strengthen his stones, ... ]
;W[kl]
C[... White will play 4, building up a moyo in the center. <= ]
)
(;B[qo]
C[Failure.  

Making a corner enclosure with 1 is overly defensive. ]
;W[mp]
LB[qo:1]
C[White now takes the strategic point of 2. Compare this diagram with the Correct Answer and you will understand why Black 1 is not an efficient move. <= ]
)
)