(;
GM[1]
SZ[19]
AW[dp][dd][jc][lb][mc][nc][ne]
AB[lc][le][pd][pf][pj][pp][jp]
TR[mc][le]
C[Problem 110. Black to play.  

In answer to Black's marked stone, White has strengthened his position at the top with his own marked stone. How should Black continue ? ]
;B[nf]
LB[ng:A]

TE[2]
C[Correct Answer.  

Attaching with Black 1 is absolutely essential so that Black can maintain a connection with his two stones on the right. If Black omits 1, White will jump to A. This black move also maps out a vast moyo on the right side, ... ]
(;W[qn]
C[... so White must invade on the lower right with 2. ]
;B[qo]
C[However, Black goes on the attack with 3 ... ]
;W[pn];B[np]
C[... and 5. ]
)
(;W[oe]
LB[nf:1]
C[Variation.  

White might respond to Black 1 ... ]
;B[of];W[pe];B[qe];W[qd]
C[... with the sequence to 6. ]
;B[rd]
C[Black sacrifices a stone when he ataris at 7 and ... ]
;W[qc];B[rf];W[rc];B[me];W[md]
C[... ends in sente with the sequence to White 12. <= ]
)
(;W[mf]
C[Variation.  

White might also play 2 here. ]
;B[me]
C[In that case Black will cut at 3, getting the advantage in the fight that follows. <= ]
)
)