Continuing the study of the relationship between TC^0,
AC^0 and arithmetic circuits, started by Agrawal et al.
(IEEE Conference on Computational Complexity'97),
we answer a few questions left open in this
paper. Our main result is that the classes DiffAC^0 and
GapAC^0 coincide, under poly-time, log-space, or log-time
uniformity. From that we can derive that under logspace
uniformity, the following equalities hold: