(;
GM[1]
SZ[19]
AW[dd][cc][fd][kc]
AB[mc][pd][qe][bd][cf][ci]
C[Problem 53. White to play.  

Black's three stones on the right are a bit thin. Where is the vital point to invade ? ]
;W[oc]
TE[2]
C[Correct Answer.  

White 1 is the vital point. ]
;B[pc]
C[After Black answers with 2, ... ]
(;W[pb];B[od];W[nc];B[nd];W[mb];B[qb];W[ob]
C[... White will link up with the moves to 9. ]
;B[md]
C[<= ]
)
(;W[od]
LB[pc:2]
C[Failure.  

Answering 2 with 3 is bad. ]
;B[oe]
C[Black forces with 4, ... ]
;W[nd];B[ob];W[nb];B[pb]
LB[ob:6]
C[... 6, and 8. ]
;W[nc]
C[After 9, White is left with bad shape. <= ]
)
)