(;AB[fe]AB[ac]AB[bc]AB[gc]AB[hc]AW[ab]AW[bb]AW[cb]AW[ba]AW[eb]AW[fb]AW[gb]AW[ga]AB[ea]AB[fc]AB[hb]AB[ha]AB[cc]AB[be]AB[ce]AB[de]AB[ee]C[It's Black's turn. Can Black kill the corner?]AB[ic]AB[jc]AB[kc]LB[ie:No]LB[he:Yes]LB[je:Ko]AP[goproblems]
(;B[db]C[NOTTHIS])
(;B[ca]C[NOTTHIS])
(;B[da]C[NOTTHIS])
(;B[fa]C[NOTTHIS])
(;B[dc]C[NOTTHIS])
(;B[ec]C[NOTTHIS])
(;B[ie];W[db]C[:(])
(;B[je];W[db]C[No, Black can kill unconditionally.])
(;B[he]C[];W[ke]C[Please show how.]
(;B[dc];W[db])
(;B[ec];W[db])
(;B[da];W[db])
(;B[fa];W[db])
(;B[db]
(;W[da]C[CHOICE]
(;B[ca]MA[da]C[Ko.])
(;B[dc]C[:)RIGHT]))
(;W[dc]C[CHOICE]
(;B[ec];W[da]C[:(])
(;B[dd];W[da]C[:(])
(;B[ca];W[da]C[?])
(;B[da];W[ec]
(;B[ca];W[fa]C[?!])
(;B[fa];W[ca]C[?!])
(;B[dd]C[White can't approach -- well done! :)RIGHT]MA[ca]MA[fa])
(;B[ed]C[White can't approach -- well done! :)RIGHT]MA[ca]MA[fa]))))))