(;AW[ba]AB[bc]AB[ac]AB[bd]AB[da]AB[db]AB[dc]AB[dd]AW[ea]AW[ec]AW[eb]AW[ed]AW[ee]AW[de]AW[ce]AW[be]AW[ae]AW[ad]AP[goproblems] (;B[cd];W[cb] (;B[ab];W[bb] (;B[ca]C[RIGHT]) (;B[cc];W[ca];B[aa];W[ca]) (;B[aa];W[ca];B[cc];W[ca])) (;B[bb];W[ab]C[Adv. ko];B[aa]C[Your solution to this puzzle involves a Ko over the A19 intersection. One might argue that a Ko is a better solution then a Seki, but this puzzle wants you to find the Seki.]) (;B[ca];W[ab]C[])) (;B[bb];W[cd];B[cc];W[ca];B[aa];W[ab]C[Disadv. ko]) (;B[ca];W[cd];B[cc];W[bb]C[]))