(;
GM[1]
SZ[19]
AW[cb][db][dc][ea][fb][gc][jc][qf][qh][qi][pj][pl][qn][rp][jp][kp][jm][cq][dp][dn][dl][cj][cg]
AB[lc][pd][qd][pf][ph][qq][pp][np][jq][iq][ho][fq][dr][ej][eg][cc][cd][dd][eb][ec][fd][de][ee]
TR[cb][db][dc][ea][fb][gc][jc]
C[Problem 86. Black to play.  

How should Black attack the marked white stones ? ]
;B[ib]
TE[2]
C[Correct Answer.  

The placement of Black 1 is on the vital point. ]
(;W[ic]
C[Blocking from above with White 2 is best. ]
;B[jb];W[hb]
C[After White 4, ... ]
;B[kc]
LB[jd:A][bb:B]
C[... Black is threatening to peep at A and hane at B, so White's stones are still insecure. <= ]
)
(;W[jb]
LB[ib:1]
C[Variation.  

In answer to Black 1, blocking at 2 seems to be a viable option, but ... ]
;B[ic];W[id];B[jd];W[hc];B[ie];W[hd];B[kd]
C[... Black builds up a large moyo in the center with the sequence to 9. Black ends in sente ... ]
(;W[bc]
C[... since White must make eyes in the corner with 10. <= ]
)
(;W[at]
C[... Black builds up a large moyo in the center with the sequence to 9. Black ends in sente ... ]
;B[hb]
LB[bc:@]
C[What happens if White neglects to play at @ ?  

Black will turn at 11. ]
;W[gb];B[kb]
C[After exchanging 13 ... ]
;W[ha]
C[... for 14, ... ]
;B[fa]
C[... Black throws in a stone at 15. Making two eyes in now problematic for White. ]
;W[ga]
C[If White captures at 16, ... ]
;B[bb]
C[... Black blocks with 17. ]
;W[he];B[if];W[hf];B[hg];W[gg]
C[White tries to get out into the center with the sequence to 22, but ... ]
;B[hh]
C[... White is trapped after Black 23. <= ]
))
)