(;
GM[1]
SZ[19]
AW[dc][cf][gq][jq][qo][qj][oc]
AB[cp][ep][op][pq][qh][pe][qd]
LB[gq:1]
C[Problem 41. Black to play.  

White makes a two-space extension with 1. What should Black do now ? ]
;B[ql]
TE[2]
C[Correct Answer.  

Black should take this opportunity to invade White's thin position on the side with 1. ]
(;W[oj]
C[If White jumps to 2, ... ]
;B[pn]
C[... Black will play 3, and the lone white stone on the lower right side is in trouble. <= ]
)
(;W[oo]
C[Variation.  

White could also attach with 2. ]
;B[no]
C[Black will hane with 3, ... ]
;W[on];B[ol]
LB[nq:B][np:A]
C[... then jump to 5. The cut at A might look worrisome, but Black can secure his stones at the bottom by playing an atari at B. (See Problem 17 in Get Strong at Invading.) <= ]
)
)