(;
GM[1]
SZ[19]
AW[dc][oc][qo]
AB[qd][qk][pq][cp]
LB[qk:1]
TR[qd]
C[Problem 20. White to play.  

Black neglects to reinforce his marked stone and pincers at 1. How should White counter this mistake ? ]
;W[pe]
TE[2]
C[Correct Answer.  

White should press Black with 1 ... ]
;B[qe];W[pf]
C[... and 3. ]
;B[qg]
C[Black's position on the right side is now rather flat. ]
;W[qf]
C[White can continue with the forcing sequence from 5 ... ]
;B[rf];W[rg];B[rh];W[pg];B[qh];W[re];B[sg];W[qc]
C[... to 13. ]
;B[rd]
TR[qk]
C[The marked black stone is now too close to his thick position above, so his stones are overconcentrated. <= ]
)
)