(;
GM[1]
SZ[19]
AW[cc][de][dh][ck][gq][jq][qp][pp][qr][pq][np][qb][oc][nd]
AB[cm][cp][eq][qq][rr][rq][rp][qn][qj][pf][qd][mc][ld][ec][hc]
TR[nd][oc][qb]
C[Problem 21. Black to play.  

The position in the top right arose from a basic joseki. How should Black attack the marked stones ? ]
(;B[pd]
TE[2]
C[Correct Answer.  

Black 1 may seem like a strange move, but it is quite effective. ]
(;W[ob]
C[White 2 is an important defensive point, but ... ]
;B[rc];W[nf];B[me];W[ne];B[ph]
C[... Black secures the right side with the sequence to 7. <= ]
)
(;W[rc]
C[If White tries to get more room in the corner with 2, ]
;B[pb]
C[... Black will attach at 3, then ... ]
;W[pc];B[qc];W[ob];B[rb];W[pa];B[ra]
C[... take the corner for himself with the sequence to 9. ]
;W[nf]
C[White still doesn't have two eyes, so she must escape with 10. ]
;B[me]
C[After 11, ... ]
;W[ne];B[ph]
LB[ob:A]
C[... Black secures the right side with 12. This result is similar to the previous variation (White 2 at A). <= ]
))
(;B[nf]
C[Failure.  

Black 1 is slack. ]
;W[rc];B[rd];W[nb]
LB[me:A]
C[White can secure her stones with the sequence to 4, and Black's territory on the right side is not as secure as it was in the Correct Answer. White is now threatening to keep Black's positions separated by moving into the center with A. <= ]
)
)