(;
GM[1]
SZ[19]
AW[de][dc][rd][qf][qi][nq][np][jp][jq][iq][fq][cn][cp][cq][cr][dr]
AB[dp][pd][pp][jc][nd][qc][qn][oq][ip][hp][hq][eq][er][dq][do][cg][cj]
LB[dc:3][de:1][cg:22][cj:10][cn:21][do:16][cp:15][cq:13][cr:19][dr:17]
LB[dq:14][fq:11][eq:20][er:18][hq:12][hp:28][ip:26][iq:25][jq:27][jp:29]
LB[np:31][nq:23][oq:30][qn:24][pp:2][jc:4][nd:6][qc:8][rd:7][qf:5]
LB[qi:9]
C[Problem 158. Black to play.  

After White stands at 31, how can Black take a decisive lead ? ]
(;B[jo]
TE[2]
C[Correct Answer.  

Black first builds influence in the center ... ]
;W[ko];B[kn];W[lo];B[ln];W[mn];B[mm]
C[... with the sequence to 7. ]
;W[nn];B[lq]
C[He then makes a placement at the vital point of White's shape with 9. ]
;W[lp]
C[White must defend with 10. ]
;B[nr]
C[Now Black can seal off the corner with 11 ... ]
;W[mr];B[or]
C[... and 13 ... ]
;W[mq]
LB[cm:B][em:A][kn:3][jo:1]
C[... in sente. Next, Black can aim at A, threatening to attach at B. However, he might first want to fix up his shape in the center by connecting between 1 and 3. <= ]
)
(;B[gc]
C[How the game continued.  

Black extended to 1 at the top and ... ]
;W[ql]
LB[jo:A][gc:1]
C[... White extended to 2 on the right side. These two points were miai, so Black 1 was not really urgent. However, with White now menacing the black stones in the lower right with 2, it is even more urgent that Black hanes at A and play the sequence in the Correct Answer. <= ]
)
)