(;AB[cc]AB[bd]AB[ad]AB[bb]AB[ba]AB[cb]AW[ae]AW[be]AW[cd]AW[dc]AW[dd]C[Kill black.]AW[fb]AP[goproblems]
(;W[ab]
(;B[aa]C[E18 also works for black--see navigation.]
(;W[ac];B[bc]
(;W[ca];B[db];W[da];B[eb];W[ea];B[fa])
(;W[da];B[db]
(;W[eb]C[RIGHT])
(;W[ea];B[eb]C[RIGHT]))
(;W[eb];B[db]
(;W[ea];B[da])
(;W[da]C[RIGHT]))
(;W[ea];B[db]
(;W[da];B[eb]C[RIGHT])
(;W[eb];B[da]))
(;W[db]C[RIGHT]))
(;W[bc];B[ac]))
(;B[eb]
(;W[db];B[da]
(;W[ec]C[RIGHT])
(;W[fc]C[RIGHT])
(;W[ea]C[This sacrifice is unnecessary];B[fa]C[This sacrifice was unnecessary]))
(;W[ec];B[db])
(;W[ea];B[da]
(;W[fa];B[db])
(;W[db];B[fa]C[This sacrifice was unnecessary]))
(;W[da];B[db];W[ea];B[ec])
(;W[ca];B[db])
(;W[fa];B[db])
(;W[fc];B[db])
(;W[bc]
(;B[db]C[RIGHT])
(;B[ac];W[bc]C[RIGHT]))))
(;W[aa];B[ab])
(;W[bc];B[ac])
(;W[ac];B[bc]
(;W[ab];B[db]
(;W[da];B[eb];W[ea];B[ec])
(;W[eb];B[da])
(;W[ca];B[da])
(;W[ea];B[da]))
(;W[aa];B[ab]))
(;W[db]C[CHOICE];B[ac])
(;W[ca]C[CHOICE];B[db])
(;W[da]C[CHOICE];B[ac])
(;W[eb];B[ac])
(;W[ea];B[ac]))