(;
GM[1]
SZ[19]
AW[dd][cc][fc][dp][cn][qq][rr][oq][or][nr][qn][pn][qk]
AB[bd][cf][ci][fq][jp][mr][nq][np][pp][op][qo][ro][qi][pd]
TR[qk][pn][qn]
C[Problem 31. Black to play.  

How can Black use his thickness to attack the marked white stones ? ]
(;B[oj]
TE[2]
C[Correct Answer.  

The knight's moves of Black 1 .. ]
;W[ol];B[mk]
LB[kd:a]
C[... and 3 are severe. White's stones can live, but Black will have built up influence in the center. He can then stake out a moyo by extending to A. <= ]
)
(;B[ok]
C[Failure.  

Capping at 1 is ineffective because Black is not using his thickness below. ]
;W[pj]
C[White breaks through Black's position with 2, and Black is left without a good follow-up move. <= ]
)
)