(;
GM[1]
SZ[19]
AW[ce][cd][cg][cm][dm][dn][do][eq][pq][qn][oc][id][if]
AB[de][ec][ef][eh][cr][cp][co][cn][kq][qd][pe][nd][kd]
TR[if][id]
C[Problem 22. Black to play.  

What should  Black do about the marked stones at the top ? Pay attention to Black's four stones on the left. ]
(;B[ih]
TE[2]
C[Correct Answer.  

Black should cap with 1. ]
;W[kf]
C[If White jumps to 2, ... ]
;B[nc]
TR[ec][de][ef][eh]
C[... Black secures the corner with 3. The important point here is that the marked stones can't be easily attacked after Black 1, while White's stones at the top are still vulnerable. <= ]
)
(;B[kf]
C[Failure.  

Chasing White into the center with Black 1 ... ]
;W[ih];B[kh]
TR[oc][ec][de][ef][eh]
C[... and 3 weakens the marked stones in the upper left. Not only are these stones in trouble, but the marked white stone in the upper right still has aji. <= ]
)
)