In this paper, we initiate the study of deterministic PIT for \Sigma^{[k]}\Pi\Sigma\Pi^{[\delta]} circuits over fields of any characteristic, where k and \delta are bounded. Our main result is a deterministic polynomial-time black-box PIT algorithm for \Sigma^{[3]}\Pi\Sigma\Pi^{[\delta]} circuits, under the additional condition that one of the summands at the top \Sigma ... more >>>