Second attempt at making this work, perhaps a bit more artificial this time.
White has played the marked stone in an attempt to get a ko - show him the error of his ways.
Thanks to Last Evolution for catching a mistake.
(;AP[goproblems]AB[cs]AB[cr]AB[cq]AB[cp]AB[bp]AW[ar]AW[bo]AW[co]AW[do]AW[dp]AW[dq]AW[dr]AB[fr]AB[ep]AB[fp]AB[en]AB[dn]AB[cn]AB[bn]AB[br]AW[ap]AB[bl]AB[gr]AW[es]TR[ap]C[Black to live unconditionally.](;B[eq];W[ds];B[aq];W[bq]C[Ko.])(;B[aq];W[bq](;B[as]C[Double ko - white can't win.RIGHT])(;B[aq]C[NOTTHIS])(;B[an];W[ds])(;B[eo];W[aq])(;B[eq];W[aq])(;B[er];W[aq])(;B[bs];W[aq]))(;B[an];W[aq];B[ao];W[bs]C[An unfavorable ko for white, but black can do better than even this.])(;B[eo];W[ds];B[aq];W[bq]C[Ko.])(;B[as];W[aq])(;B[er];W[ds](;B[aq]C[Ko])(;B[as]C[Ko]))(;B[ds];W[bq]))