(;AB[bc]AB[bd]AB[cd]AB[dd]AB[dc]AB[db]AB[ec]AB[fc]AB[gc]AW[bb]AW[cb]AW[cc]AW[eb]AW[fb]AW[gb]AW[hc]AW[hd]AW[gd]AW[fd]AW[ed]AW[de]AW[ce]AW[be]AP[goproblems](;B[ca];W[ad](;B[ab]C[RIGHT])(;B[ba];W[ab]))(;B[ab];W[ba](;B[da];W[ad];B[ca]C[RIGHT])(;B[ac]C[Black is dead! White can either play C19 any time for a bulky 5 dead shape or D19 after which Black cannot approach.]))(;B[ba];W[ca];B[da];W[aa];B[ac];W[ea]C[CHOICE])(;B[da];W[ac](;B[ad];W[aa]C[Approach-move ko.])(;B[ab];W[aa];B[ad];W[ae]C[Ko])(;B[ba];W[ad];B[ab];W[aa]C[Ko])))