(;
GM[1]
SZ[19]
AW[cd][fc][nc][nb][pc][qc][qm][ro][qq][nq][mp][iq][fq][fp]
AB[dp][pp][lc][me][qd][pd][od][pj][oq][np][mq][no][dn][ci][kq][eq]
TR[fp]
C[Problem 156. Black to play.  

How should Black respond after White plays the marked stone (White 4 in the game continuation of Problem 152) ? ]
(;B[jo]
TE[2]
C[Correct Answer.  

The black stones at the bottom have bad aji, so Black should strengthen them by attacking the white group with 1 ... ]
;W[io];B[in]
C[... and 3. ]
;W[ho];B[cf]
C[He can then take the key point at 5 on the left side. <= ]
)
(;B[cf]
C[How the game continued.  

Black extended to 1 without strengthening his stones at the bottom, so ... ]
;W[jo]
C[... White took her opportunity to stabilise her stones there by playing 2. ]
;B[fr];W[gr];B[er];W[ck];B[cm];W[ek]
C[The game continued to White 8. <= ]
)
)