sentences:  In circuit complexity, FO(ARB) where ARB is the set of all predicates, the logic where we can use arbitrary predicates, can be shown to be equal to AC0, the first class in the AC hierarchy.Indeed, there is a natural translation from FO's symbols to nodes of circuits, with formula_25 being formula_26 and formula_27 of size .FO(BIT) is the restriction of AC0 family of circuit constructible in alternating logarithmic time.