(;
GM[1]
SZ[19]
AW[ch][jc][lc][pc][qb][qe][qf]
AB[dc][cf][hc][nc][pb][pe]
LB[qb:2][pb:1]
C[Problem 94. Black to play.  

White answers Black 1 by blocking at 2. What should Black do ? ]
(;B[pd]
TE[2]
C[Correct Answer.  

Black 1 is the vital point. <= ]
)
(;B[oc]
LB[pd:@]
C[Failure.  

Of course, Black would like to play at 1, but he cannot do so unless he has played @ in the Correct Answer. ]
;W[pd]
C[Now White takes the point 2, and Black's shape has collapsed. <= ]
)
)