(;
GM[1]
SZ[19]
AW[cc][dd][df][dp][nc][pb][qb][qc][qd][qf][pf][ph][og][ng][mf][lf]
AB[pp][db][fc][fe][lc][nd][ob][oc][pc][pd][pe][of][nf][qh][pi][mg]
LB[lf:A]
TR[mg]
C[Problem 108. Black to play.  

In answer to the marked stone, White extends to A. What should Black do next ? ]
(;B[nh]
TE[2]
C[Correct Answer.  

Black 1 is the key point. ]
(;W[rg]
C[In answer to Black 1, White must defend her corner territory with 2. ]
;B[mh];W[kg];B[ki]
C[Black chases the group at the top with 5, making influence in the center. ]
;W[ig];B[jd]
C[He then defends the top with 7. Black should be quite satisfied with this result. <= ]
)
(;W[mh]
C[Suppose White subdues this stone with 2 ... ]
;B[lg];W[ni]
C[... and 4. ]
;B[qe]
C[Black would then cut through with 5 ... ]
;W[re];B[rf]
C[... and 7, ... ]
;W[rg];B[qg]
LB[pg:A]
C[... then atari at 9. White can't play at A because she is short of liberties, so ... ]
;W[sf]
C[... she has to capture with 10. Next, ... ]
;B[pg]
C[... Black ataris with 11 ... ]
;W[oh];B[oi]
C[... and 13, and ... ]
;W[nh];B[lh];W[nj];B[rf]
C[... and the sequence continues up to Black 17. White ends up with a weak group in the center and two weak stones at the top. Black has a huge advantage. <= ]
))
(;B[mh]
C[Failure.  

Black 1 is ineffective. ]
;W[oi]
C[Even though the sequence from White 2 ... ]
;B[pj];W[oj];B[pk];W[ok];B[pl]
C[... Black 7 gives Black profit on the right side, ... ]
;W[kg]
C[... Blacks two stones in the center are under attack when White plays 8. Comparing this diagram with the Correct Answer, it should be clear that this result is unsatisfactory for Black. <= ]
)
)