(;
GM[1]
SZ[19]
AW[cn][co][dm][ek]
AB[jp][jd][pj][dj][dp][pd][pp][dd][jj][cp][dn][en]
LB[ek:7][dm:3][cn:1][co:5][cp:6][dn:2][en:4]
C[Problem 23. Black to play.  

In this nine-stone game, Black played the attach-and-extend joseki with the sequence to 6. White 7 was an unusual move. How should Black respond ? ]
(;B[ej]
TE[2]
C[Correct Answer.  

Black should push up with 1, ... ]
;W[fk]
C[... forcing White to extend to 2, ... ]
;B[dk]
C[... then turn at 3. ]
(;W[em]
C[If White 4, ... ]
;B[fp]
C[... Black secures the bottom with 5. ]
;W[fj]
C[If White 6 next, ... ]
;B[fi];W[gi];B[fh]
C[... the sequence to Black 9 follows. <= ]
)
(;W[dl]
C[White gets a defective shape is she plays 4 here. <= ]
))
(;B[dk]
C[How the game continued.  

You might think that Black 1 would give the same result as the Correct Answer, but, ... ]
;W[em]
(;B[fm];W[fl]
LB[em:2]
C[... after 2 and 4, ... ]
;B[gm];W[dg]
C[... White attacked the two black stones, which were now heavy, with 6. <= ]
)
(;B[fp]
C[If Black had played 3 here, ... ]
;W[dg]
C[... White would still have attacked with 4. <= ]
))
)