(;AB[ca][da][db][cc][bb][bd][ad][ae]AW[af][be][ce][cd][dd][dc][ed][fc][eb][ea][bf]
C[Can b tenuki here?
]LB[hd:A]AP[MultiGo:3.8.6]SZ[19]
(;B[ac]C[RIGHT
CORRECT. White only has one ko threat against the corner])
(;B[ab]C[RIGHT
NOT BEST MOVE. White has two ko threats against the corner])
(;B[hd]C[wrong. w can get a ko.];W[ab]C[w has made a ko for the corner.]
(;B[ac];W[bc]C[b dies])
(;B[ba]C[not even a ko];W[bc];B[ac];W[bc]C[dead])
(;B[bc];W[ba]C[ko])
(;B[aa];W[ba]C[ko]))
(;B[aa]C[RIGHT
CORRECT. White has only one ko threat against the corner
])
(;B[ba]C[RIGHT
NOT BEST MOVE. White has two ko threats against the corner])
(;B[bc]C[RIGHT
NOT BEST MOVE. This leaves white two ko threats against the corner]))