(;
GM[1]
SZ[19]
AW[fc][kc][nb][qd][rd][qf][ph][ql][dr][fr][hq][go][cn][bl][cl][ak][ck][dk][ej]
AB[dp][pd][pp][dd][db][df][gd][hc][nd][pc][qc][rc][qn][kq][fp][co][dn][bm][cm][bk][cj][bi]
TR[ak]
C[Problem 137. Black to play.  

White has just ataried with the marked white stone. How should Black respond ? ]
(;B[oq]
TE[2]
C[Correct Answer.  

Defending the lower right with 1 is a big move; the corner alone is worth 15 points. ]
;W[bj]
C[If White captures a stone with 2, ... ]
;B[qj]
C[... Black will invade at 3, destroying White's only substantial territory. Black has an unassailable lead. <= ]
)
(;B[bj]
C[If Black connects.  

If Black connects at 1, ... ]
;W[pq]
C[... White can attach at 2 and live in the corner ... ]
;B[oq];W[qp];B[po];W[pr];B[or];W[ro];B[rn];W[rr]
C[... with the sequence to 10. White's territory there is worth 9 points, so Black 1 in the Correct Answer is worth more than 25 points. ]
;B[qj]
C[In any event, Black is still in the lead and the invasion at 11 is his biggest move. <= ]
)
)