(;
GM[1]
SZ[19]
AW[dc][ed][oq][qp][nc][kc][pb]
AB[ce][ci][co][dq][qj][pd][qc][pf]
C[Problem 163. White to play.  

The only moves left are extensions on the side. Where should White play ? ]
(;W[iq]
TE[2]
C[Correct Answer.  

White should extend all the way to 1. ]
(;B[qm]
C[If Black 2, ... ]
;W[fq]
C[... White can make a checking extension with 3. <= ]
)
(;B[gq]
C[If Black 2 here, ... ]
;W[ql]
C[... White takes the last big extension at 3. <= ]
))
(;W[ip]
C[Failure.  

White must not make a high extension to 1, ... ]
;B[gq]
C[... because  Black 2 threatens an invasion on the lower side. <= ]
)
(;W[ql]
C[Failure.  

The checking extension on the ride side with 1 is not necessarily bad, but ... ]
;B[jq]
LB[ql:1]
C[... Black will extend to 2 and make an ideal double-wing formation from his corner enclosure in the lower left. For that reason, White 1 must be criticised. <= ]
)
)