(;
GM[1]
SZ[19]
AW[ed][fc][gd][kc][dp][lp][mq][mo][pn][qk][pp][qp][qo][rp][rq]
AB[cd][ec][dc][cf][fq][jq][po][oo][op][oq][qq][qr][rr][oc][qd]
C[Problem 169. Black to play.  

In this position it is urgent for Black to settle his stones in the lower right. Where should he play ? ]
(;B[nr]
LB[sr:B][lr:A]

TE[2]
C[Correct Answer.  

Black should defend his stones with 1. Black doesn't have to worry about their safety anymore because he can either link up his stones on the left with A or make two eyes with B. ]
;W[on]
C[If White blocks with 2, ... ]
;B[cn]
LB[nn:A]
C[... Black is happy just to play the approach move of 3. Black is threatening to hane at A, so White cannot avoid a disadvantageous fight. <= ]
)
(;B[on]
C[Failure.  

It might seem more natural for Black to prevent the blockade and advance into the center with 1 ... ]
;W[pm];B[om]
C[... and 3, but ... ]
;W[pq]
C[... White could force with 4 ... ]
;B[pr];W[nr]
C[... and 6. ]
;B[or];W[mm]
C[Black's group doesn't have two eyes and White goes on the attack with 8. ]
;B[ol]
C[If Black 9 next, ... ]
;W[pj]
C[... White will play at 10. <= ]
)
)