Decoupling inequalities and some mean-value theorems

The purpose of this paper is to present some further applications of the general decoupling theory from [B-D1, 2] to certain diophantine issues. In particular, we concider mean value estimates relevant to the Bombieri-Iwaniec approach to exponential sums and arising in the work of Robert and Sargos [R-S]. Our main input is a new mean value theorem.