(;
GM[1]
SZ[19]
AW[dd][dc][df][ch][bg][co][dp][gq][jq][rp][rn][sn][sm][qm][ql][rl][qk][qj][pj][qi][ri][qh][qd][rd][qa][pa][pb][pc][oc][od][oe][mb][mc][lc][kc][kd][kb][jb][hb][hj][nk][gk][hk][cr][dq][hp][ho][cn][dm][cl][dl]
AB[bh][cj][cm][oq][qp][qn][qo][ro][so][rh][sg][rf][re][qe][pe][pd][qc][rc][qb][ra][ne][nf][md][ld][nb][ib][ic][jc][jd][je][ke][fc][fe][gi][pk][ok][oj][ol][pi][ph][gj][dr][eq][fp][gp][fn][dn][hm][em][jm][fk]
LB[jm:A]
C[Problem 123. Black to play.  

This is the position that arose in the game of Problem 121. Black just jumped to A. What should White do ? ]
;W[gm]
LB[jm:A]

TE[2]
C[Correct Answer.  

Black A in the problem diagram is thin. When White attaches with 1 ... ]
;B[gn];W[hn]
C[... and cuts with 3, the black stones in the center are cut off from their allies on the left. ]
;B[hl]
C[Black resists with 4, but ... ]
;W[gl]
C[Black must answer White 5 ... ]
;B[el]
C[... with 6, ... ]
;W[jl];B[in];W[hi];B[gh];W[km]
C[... and Black's position collapses when White blocks with 11. <= ]
)
)