The power of the middle bit

The class of languages that can be recognized in polynomial time with the additional information of one bit from a P function is studied. In particular, it is shown that every Mod/sub k/P class and every class contained in PH are low for this class. These results are translated to the area of circuit complexity using MidBit (middle bit) gates. It is shown that every language in ACC can be computed by a family of depth-2 deterministic circuits of size 2 to the (log n)/sup c/ power with a MidBit gate at the root and AND-gates of fan-in (log n)/sup c/ at the leaves. This result improves the known upper bounds for the class ACC.<
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