(;
GM[1]
SZ[19]
AW[ch][jc][je][lc][ob][pa][qb][qc][pc][rd][re][qe][qf]
AB[dc][cf][hc][nc][oc][rb][rc][pe][pd][qd][ne]
LB[pa:1][pb:A]
C[Problem 109. Black to play.  

White has captured the black stone at A captures with 1. What should Black do now ? ]
(;B[ra]
TE[2]
C[Correct Answer.  

Black should play 1 ... ]
(;W[qa];B[nb]
C[... and 3, ... ]
;W[sc]
LB[ma:B][na:A]
C[... then leave the situation as it is. After 4, Black A (or Black B, threatening ko) could later become double threats against the white groups on the left and the right. <= ]
)
(;W[nb]
C[If White 2, ... ]
;B[qa]
C[... Black plays 3 and White collapses. <= ]
))
(;B[nb]
C[Failure.  

Simply playing Black 1 is lukewarm. ]
;W[ra]
C[White plays 2 and there is no longer any danger to her stones in the corner. <= ]
)
)