(;
GM[1]
SZ[19]
AW[dc][fc][gd][ed][ce][ee][co][qp][nq][nc][md][od][nf][oe]
AB[cc][db][eb][ec][fd][dq][ep][qd][pc][oc][nb][mb][ne][pf]
C[Problem 90. Black to play.  

At the top, Black has taken profit while White has gotten influence in the center. Taking the whole board into consideration, where is Black's best move ? ]
(;B[op]
TE[2]
C[Correct Answer.  

Black should play 1, breaking the ladder. ]
;W[fe]
C[White has to capture with 2, ... ]
;B[oq]
TR[mb]
C[... so Black can then play 3, breaking through White's corner enclosure. Of course, White becomes thick when she captures, but the marked black stone serves to diminish the effect of this thickness. <= ]
)
(;B[cl]
C[Failure.  

Locally, the pincer of Black 1 is a good point, but ... ]
;W[fe]
C[... White will capture with 2 and the aji of the ladder-breaking move disappears. ]
;B[dn]
C[Although Black will become thick with 3 ... ]
;W[cn];B[dm]
C[... and 5, White is also thick at the top, so it balances out. ]
;W[bq]
LB[cn:4]
C[Moreover, White can live in the corner with 4 and 6. <= ]
)
)