(1)a b f
0 0 0
0 1 1
1 0 1
1 1 0
(2) a b c f
0 0 0 1
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 1
1 0 1 1
1 1 0 1
1 1 1 1