(;AB[bb]AW[aa]AW[bc]AW[bd]AW[ad]AW[cc]AW[dc]AW[ec]AW[eb]AW[da]AB[ea]AB[fa]AB[fb]AB[fc]AB[fd]AB[ed]AB[dd]AB[cd]AB[ae]AB[be]AB[cf]AP[goproblems]
(;B[cb];W[ab]
(;B[db]C[RIGHT])
(;B[ca];W[ba]
(;B[ac];W[ab]
(;B[db];W[ba]C[Play at E14 if you need a ko threat smaller that what the corner is worth.]LB[ef:T]
(;B[ac]C[RIGHT])
(;B[da]C[RIGHT])
(;B[ef];W[da]))
(;B[aa];W[ba]C[Ko])
(;B[ba]C[RIGHT]))
(;B[db];W[da]))
(;B[ba];W[db];B[ac];W[ab]C[CHOICE]))
(;B[ca];W[cb];B[db]C[Adv. koCHOICE])
(;B[ab];W[cb];B[ba];W[ca]C[CHOICE])
(;B[ba];W[ab];B[cb];W[db];B[ac];W[ab]C[CHOICE]))