(;AW[ca]AW[bb]AB[cb]AB[ac]AB[bd]AB[ae]AW[be]AW[bf]AW[af]AW[ag]AW[ah]AW[bh]AW[cg]AW[cf]AW[eg]AW[ff]AW[ge]AW[hd]AW[hc]AW[gb]AW[fb]AW[eb]AW[ec]AW[da]AB[db]AB[dc]AB[dd]AB[ed]AB[fd]AB[fc]AB[gc]AB[cd]AB[ce]C[What's the best black can do?]AP[goproblems] (;B[ba]C[White connects at E19. A19 is only here to show that white can't avoid the ko.] (;W[ea] (;B[ab];W[aa]MA[ba]C[Yup, Ko - Well done! ;)RIGHT];B[ba]C[NOTTHIS]) (;B[bc];W[aa] (;B[ab];W[ba]C[Black's dead!]) (;B[hb];W[ib];B[ab];W[ba]C[Black's dead!])) (;B[aa];W[ab] (;B[bc];W[ba]C[Black's dead!]) (;B[ba];W[aa] (;B[bc];W[ba]C[Black's dead!]) (;B[hb];W[ib];B[bc];W[ba]C[Black's dead!])) (;B[hb];W[ib] (;B[bc];W[ba]C[Black's dead!]) (;B[ba];W[aa];B[bc];W[ba]C[Black's dead!]))) (;B[hb];W[ib] (;B[ab];W[aa]MA[ba]C[Yup - It's a ko - but H18 is a waste of a ko threat..!];B[ba]C[NOTTHIS]) (;B[bc];W[aa]C[Black's dead!];B[ab];W[ba]C[Black's dead!]) (;B[aa];W[ab]C[Black's dead!] (;B[bc];W[ba]C[Black's dead!]) (;B[ba];W[aa];B[bc];W[ba]C[Black's dead!])) (;B[ha];W[ia] (;B[ab];W[aa]MA[ba]C[Yup - It's a ko - but H18 is a waste of a ko threat..!];B[ba]C[NOTTHIS]) (;B[bc];W[aa]C[Black's dead!]) (;B[aa];W[ab]C[Black's dead!])))) (;W[aa]C[This just lets black live, without a ko.];B[ea];W[fa];B[ab] (;W[ea];B[bc];W[ba];B[hb]C[White can't avoid the ko.]) (;W[ba];B[bc];W[ea];B[hb]C[White can't avoid the ko.]) (;W[hb];B[bc];W[ea];B[ba]C[White can't avoid the ko.]))) (;B[bc];W[ba]C[Black's dead!]) (;B[ab];W[ba]C[Black's dead!]) (;B[aa];W[ba]C[Black's dead!]) (;B[ea];W[ba]C[Black's dead!]) (;B[hb];W[ib];B[ba];W[ea] (;B[ab];W[aa]C[Yup - It's a ko - but H18 is a waste of a ko threat..!]MA[ba];B[ba]C[NOTTHIS]) (;B[bc];W[aa]C[Black's dead!];B[ab];W[ba]C[Black's dead!]) (;B[aa];W[ab]C[Black's dead!] (;B[bc];W[ba]C[Black's dead!]) (;B[ba];W[aa];B[bc];W[ba]C[Black's dead!])) (;B[ha];W[ia] (;B[ab];W[aa]C[Yup - It's a ko - but H18 is a waste of a ko threat..!]MA[ba];B[ba]C[NOTTHIS]) (;B[bc];W[aa]C[Black's dead!]) (;B[aa];W[ab]C[Black's dead!]))) (;B[ef]C[NOTTHIS]))