(;
GM[1]
SZ[19]
AW[db][fc][hc][jc][qf][pf][qj]
AB[cc][dd][df][lc][nd][pd][qe]
C[Problem 143. White to play.  

Black's position here is much tighter. Where should White invade ? ]
(;W[nb]
TE[2]
C[Correct Answer.  

Invading with 1 is a good move. ]
(;B[pb]
C[If Black defends the corner with 2, ... ]
;W[mc];B[md];W[lb]
LB[mc:3]
C[... White links up with 3 and 5. <= ]
)
(;B[mc]
C[Variation.  

If Black prevents White from linking up on the left by playing 2, ... ]
;W[qc]
LB[mc:2][nb:1]
C[... White plays on the 3-3 point with 3. With the exchange of 1 for 2 in place, this is an effective move. <= ]
))
(;W[qc]
TE[2]
C[Correct Answer.  

A direct invasion here is also possible. <= ]
)
)