(This problem has some nasty variations. If i missed interesting ones, feel free to comment.)
(;AB[ba]AB[bc]AB[cb]AB[db]AW[eb]AW[fc]AW[gb]AW[fd]AW[hc]AW[ic]AW[kc]AW[jd]AW[je]AW[if]AW[hf]AW[hh]AW[gi]AW[ei]AW[dh]AW[cg]AW[df]AW[ce]AW[cd]AW[cc]AW[dc]AB[ec]AB[ed]AB[ee]AB[ef]AB[eg]AB[fe]AB[fg]AB[gf]AB[gd]AB[hd]AB[id]AB[hb]AP[goproblems]
(;B[gc]
(;W[fb]C[CHOICE]
(;B[ib];W[jc]
(;B[ea];W[jb]
(;B[fa];W[ia];B[ga]C[RIGHT])
(;B[ga];W[ia];B[fa]C[RIGHT])
(;B[ha]C[RIGHT]))
(;B[ga];W[jb]
(;B[ea];W[ia];B[fa]C[RIGHT])
(;B[fa];W[ia];B[ea]C[RIGHT])
(;B[ha]C[RIGHT]))
(;B[fa];W[jb]
(;B[ea];W[ia];B[ga]C[RIGHT])
(;B[ga];W[ia];B[ea]C[RIGHT]))
(;B[jb]C[NOTTHIS])
(;B[ha]C[RIGHT]))
(;B[ea];W[ib])
(;B[ga];W[ib]))
(;W[fa];B[fb];W[fc];B[he]C[Black can at least live. Better is to play at the marked point first.RIGHT]MA[ib]))
(;B[fb];W[fa]
(;B[gc];W[he]
(;B[fb];W[fc]
(;B[ib];W[jc];B[da];W[ea]
(;B[fd];W[jb]C[Ko. Indeed, this ko is not flavorable for white, but the solution does not contain any ko.])
(;B[jb];W[kb];B[fd];W[ja]C[Ko. Indeed, this ko is not flavorable for white, but the solution does not contain any ko.]))
(;B[da];W[ib]))
(;B[ib];W[jc];B[fb];W[fc];B[da];W[ea]
(;B[fd];W[jb]C[Ko. Indeed, this ko is not flavorable for white, but the solution does not contain any ko.])
(;B[jb];W[kb];B[fd];W[ja]C[Ko. Indeed, this ko is not flavorable for white, but the solution does not contain any ko.])))
(;B[da];W[gc]C[Black dies.]))
(;B[ib];W[gc])
(;B[ea];W[fb]
(;B[ib];W[gc])
(;B[gc];W[ib]))
(;B[da];W[gc])
(;B[fa];W[fb])
(;B[ga];W[gc]))