(;
GM[1]
SZ[19]
AW[bc][cc][dc][ed][ee][cf][cg][di][dp][po][pm][qn][qi]
AB[bb][db][eb][ec][bd][cd][dd][ce][pq][nq][qp][qo][qd][oc]
C[Problem 66. White to play.  

There is a wide space between White's thickness on the upper left and her stone below. However, Black has a good attacking move on the upper right. What should White do ? ]
(;W[dn]
LB[qf:A]

TE[2]
C[Correct Answer.  

White might be tempted to extend to A on the right side, but, in this case, it is better to strengthen the stone in the lower left with 1. ]
;B[qg]
C[If Black 2, ... ]
;W[mp]
C[... White will play 3 ... ]
;B[np];W[mn]
LB[ql:B]
C[... and 5, mapping out a large-scale moyo. Note that White 5 indirectly defends against the invasion at B. <= ]
)
(;W[qf]
C[Failure.  

If White extends to 1, ... ]
;B[cn]
C[... Black approaches at 2 and breaks up White's position on the left side ... ]
;W[co];B[dn];W[fp];B[ck]
C[... with the sequence to 6. The effectiveness of White's thickness above is now neutralised. <= ]
)
)