Middle-Game: Section 1. Pr. 7. B 2 play. B has a tesuji by shich he can either rescue his isolated stone in the corner or prevent W from linking up his 4 stones at the center top.
(;AB[qd]AW[pe]AW[qe]AW[re]AB[qg]AB[og]AW[pc]AW[ob]AW[mb]AW[lb]AW[lc]AW[ld]AB[nb]AB[mc]AB[md]AB[me]AB[le]AB[je]AB[ic]AP[goproblems]
(;B[od];W[pd];B[na]C[Correct answer. Peeping w/ B 1 is the key move. W has no choice but 2 defend at 2 & limit his loss. B can now isolate the 4 W stones at the top with 3.RIGHT]LB[od:1]LB[pd:2]LB[na:3])
(;B[oc];W[na];B[pd];W[od]C[Wrong answer. B 1 fails. B may try 3 in response to 2, but after W 4 he has no follow-up.]LB[oc:1]LB[na:2]LB[pd:3]LB[od:4])
(;B[na];W[nc]
(;B[nd];W[oc]C[B fails :-(])
(;B[od];W[pd];B[oc]C[RIGHT])))