(;
GM[1]
SZ[19]
AW[pp][ph][ic][kc][lc][mc][oc][pc]
AB[cd][dq][qe][od][ne][ld][kd][jd]
TR[ph]
C[Problem 106. Black to play.  

The marked white stone is in the shadow of Black's thick wall at the top. How should Black attack it ? ]
(;B[pk]
TR[ph]

TE[2]
C[Correct Answer.  

Black doesn't want to pincer too severely because White might decide to sacrifice her marked stone. Therefore, Black plays a two-space pincer with 1. ]
;W[ni]
C[If White plays 2, ... ]
;B[qn]
C[... Black approaches with 3. ]
;W[qo];B[pn];W[np];B[nk];W[li];B[he]
C[With the sequence to 9, Black is making good use of his thickness at the top. <= ]
)
(;B[qn]
LB[pk:@][np:A]
C[Failure.  

When Black plays the approach move of 1, he thinks that White is going to respond with A, enabling him to pincer the white stone by extending to @. But this is too much to expect. ]
;W[ql]
C[White would pincer at 2 instead, ... ]
;B[qq]
C[... and Black has no other alternative but to invade at 3. ]
;W[qp];B[pq];W[op];B[rp];W[ro];B[rq];W[qo];B[nq]
C[With the joseki to 11, White has made thickness at the bottom, effectively neutralising Black's wall at the top. <= ]
)
)