There is a story behind the problem, but telling it here would be a hint. Maybe you want to take a look at the problem source. Comments are welcome.
(;AB[ca]AB[cb]AB[cc]AB[cd]AB[be]AB[ad]AW[ae]AW[af]AW[bg]AW[ce]AW[cf]AW[ba]AW[dd]AW[dc]AW[db]AW[fb]AW[ch]LB[fd:D]LB[ff:K]LB[fh:L]C[What is the status of the black group? Is it dead (D)? Or can black make a ko for life (K)? Or can black live without ko (L)?FORCE]AP[goproblems]
(;B[fh];W[hh]C[Please show how black can live without ko.]
(;B[bb]C[];W[bd]
(;B[bc]
(;W[bf]
(;B[aa]C[Good!RIGHT])
(;B[bd];W[ab]C[Ko!])
(;B[ab];W[bd]C[Ko!]))
(;W[ab]C[];B[ac]C[(Note that this is not a ko.)RIGHT]))
(;B[ac];W[aa])
(;B[aa];W[ac])
(;B[ab];W[bf]))
(;B[ab];W[bc]
(;B[bd];W[bb]C[Black is dead. It is not seki, because white could force black to fill A17 by filling the outside liberties.])
(;B[bb];W[bd];B[ac];W[bd]))
(;B[bd];W[bb];B[ab];W[bc]C[Black is dead. It is not seki, because white could force black to fill A17 by filling the outside liberties.])
(;B[bc];W[ab])
(;B[aa];W[bb])
(;B[ac];W[bb]))
(;B[ff];W[hf]C[Sorry. Look again!])
(;B[fd];W[hd]C[Sorry. Look again!]))