(;
GM[1]
SZ[19]
AW[db][eb][gc][hc][dc][de][ce][qf][of][mf][qi][or][nr][nq][mp][jp][ip][hq][fo][di][fm][dn][cp][dq][eq]
AB[ec][ed][ee][gd][hd][id][oc][qd][qk][ok][oi][pn][pp][pr][oq][hp][gp][fp][fq][ep][hn][hl][fk][dk]
TR[mf][of][qf][qi]
C[Problem 55. Black to play.  

How should Black attack the four marked stones in the upper right ? ]
;B[pg]
TE[2]
C[Correct Answer  

Black should peep with 1, ... ]
;W[pf];B[rh]
C[... then make a placement at 3. ]
(;W[od]
C[White can no longer make two eyes on the right side, so she has to switch to the top and ... ]
;B[pc];W[nc];B[nb];W[mc];B[mb];W[lc]
C[... play the sequence to 10, inducing Black to secure the corner. ]
(;B[fi]
C[Black ends in sente, so he takes the key point of 11 to reach out to his stones above and to start building a moyo in the center. <= ]
)
(;B[nn]
C[Failure.  

The aim of 11 here is to map out a moyo with ... ]
;W[fi];B[lo]
C[... 13 and ... ]
;W[lp];B[jn]
C[... 15, but ... ]
;W[gk]
C[... White attaches at 16 and a sharp exchange ensues. ]
;B[gj];W[gl];B[fj]
(;W[hk]
C[White turns at 20 and Black's moyo becomes thin. <= ]
)
(;W[gh]
C[... White could also play 20 here attacking Black's stones at the top. ]
;B[hk]
C[Black would respond at 21. <= ]
)))
(;W[re]
C[Variation.  

The placement of Black 3 is a flexible move. For example, if White exchanges 4 ... ]
;B[rd]
C[... for 5, ... ]
;W[qh];B[ri]
LB[qg:A][qh:6]
C[... Black can crawl to 7 if White plays 6. Since White has to defend her defect at A, Black will end in sente. <= ]
)
)