This is the most difficult of the problems in this collection. However, it's a beautiful problem, with some impressive moves. The point is to aim at a gomoku-nakade, but you have to be careful not to get a seki. The villain complicating matters is White's hane.
(;AB[kp]AB[jq]AB[iq]AB[ir]AB[lp]AB[mp]AB[np]AB[op]AB[pp]AB[pq]AB[pr]AB[rr]AW[jr]AW[kr]AW[kq]AW[lq]AW[mq]AW[nq]AW[or]AW[oq]AW[ps]C[Black to play and kill White ]AP[goproblems]
(;B[ns]
(;W[os];B[mr]
(;W[ls];B[js]C[Black has to start with the placement at 1. If White 2, Black plays 3, and killing White is quite simple. If White 'a', Black 'b'; if White 'b', Black 'a' creates a gomoku-nakade.
RIGHT]LB[ns:1]LB[os:2]LB[mr:3]LB[ls:a]LB[js:b])
(;W[js];B[ls]LB[ns:1]LB[os:2]LB[mr:3]LB[js:b]LB[ls:a]C[Black has to start with the placement at 1. If White 2, Black plays 3, and killing White is quite simple. If White 'a', Black 'b'; if White 'b', Black 'a' creates a gomoku-nakade.
RIGHT]))
(;W[js]
(;B[ls]LB[ns:1]LB[js:2]LB[ls:3]LB[mr:a]LB[os:b]C[If White descends at 2, Black counters by jumping to 3: this move is the highlight of this problem. Next, 'a' and 'b' are miai, so White is dead. Black 3 is an inspired move. RIGHT])
(;B[os];W[ls];B[mr];W[nr]LB[ms:a]LB[os:1]LB[ls:2]LB[mr:3]LB[nr:4]TR[ps]C[If Black hastily cuts at 1, White counters with 2 and lives: after White 4, Black can't connect at 'a' — note the efficacy of the marked white stone.
CHOICE])))
(;B[mr];W[js];B[ns];W[ls]LB[mr:1]LB[js:2]LB[ns:3]LB[ls:4]C[If Black starts with 1, White descends at 2. If Black 3, White 4 leads to the same result as in the previous diagram. If Black plays 3 at 4, White 3 creates a seki.
CHOICE]))