(;AB[bc]AB[bd]AB[ce]AB[de]AB[ee]AB[fe]AB[fd]AB[fc]AB[gc]AB[gb]AW[fb]AW[ed]AW[ec]AW[dd]AW[cd]AW[cc]AW[bb]AW[ab]AB[bf]AB[db]AW[be]C[White to play. Black has one external ko threat, White has no external ko threat.]AP[goproblems]
(;W[eb];B[cb]
(;W[ba]
(;B[ea]C[CHOICE]
(;W[fa];B[ca];W[da];B[he]C[Respond to the ko threat.]TR[ie]
(;W[ie];B[ea]C[Please finish the ko. If you want to tenuki you can play at A15.]
(;W[ad];B[ae];W[da]C[RIGHT])
(;W[ac];B[ae];W[da]C[RIGHT])
(;W[ae];B[ga];W[da]C[This situation would be worse for White, if Black could capture the ko again at some point. Under the given circumstances this answer is correct.RIGHT]))
(;W[hd]C[NOTTHIS])
(;W[id]C[NOTTHIS])
(;W[jd]C[NOTTHIS])
(;W[je]C[NOTTHIS])
(;W[if]C[NOTTHIS])
(;W[jf]C[NOTTHIS])
(;W[hf]C[NOTTHIS]))
(;W[ca];B[fa]C[oops])
(;W[da];B[ca];W[fa];B[ga];W[da];B[he]C[Respond to the ko threat.]TR[hd]
(;W[hd];B[ea]
(;W[ad];B[dc]C[oops])
(;W[ac];B[dc]C[oops]))
(;W[hc]C[NOTTHIS])
(;W[ic]C[NOTTHIS])
(;W[id]C[NOTTHIS])
(;W[ie]C[NOTTHIS])
(;W[gd]C[NOTTHIS])
(;W[ge]C[NOTTHIS])))
(;B[da];W[ea]TR[ac]TR[be]C[RIGHT]))
(;W[ca];B[da]
(;W[ba];B[fa]C[oops])
(;W[ea];B[ba]C[White can't approach.])
(;W[dc];B[ba]C[White can't approach.])
(;W[aa];B[fa]C[oops]))
(;W[da];B[ca]
(;W[ba];B[ea];W[fa];B[ga];W[da];B[he]C[Respond to the ko threat.]TR[hd]
(;W[hd];B[ea]
(;W[ad];B[dc]C[oops])
(;W[ac];B[dc]C[oops]))
(;W[hc]C[NOTTHIS])
(;W[ic]C[NOTTHIS])
(;W[id]C[NOTTHIS])
(;W[ie]C[NOTTHIS])
(;W[gd]C[NOTTHIS])
(;W[ge]C[NOTTHIS]))
(;W[ea];B[ba]C[White can't approach.])
(;W[fa];B[ga];W[ba];B[ea]
(;W[ad];B[dc]C[oops])
(;W[ac];B[dc]C[oops]))
(;W[dc];B[ea]C[oops]))
(;W[dc];B[fa])
(;W[fa];B[ga]
(;W[ca];B[da];W[ba]C[White can't approach.])
(;W[da];B[ca];W[ba];B[ea]
(;W[ad];B[dc]C[oops])
(;W[ac];B[dc]C[oops]))
(;W[ba];B[da]C[White can't approach.]))
(;W[ea];B[ba]
(;W[ca];B[da]C[White can't approach.])
(;W[da];B[ca]C[White can't approach.])
(;W[dc];B[ca]C[White can't approach.])))
(;W[cb];B[eb]C[White has only one eye.])
(;W[ac]C[NOTTHIS])
(;W[ad]C[NOTTHIS])
(;W[ea];B[eb]C[oops])
(;W[ca];B[eb]C[White has only one eye.])
(;W[da];B[eb]C[oops])
(;W[fa];B[eb]C[oops])
(;W[ba];B[eb]C[White has only one eye.]))