We estimate double exponential sums of the form ![\begin{equation*}S_a(\,{\mathcal X},\,{\mathcal Y}) = \sum_{x \in \,{\mathcal X}... ...\in \,{\mathcal Y}} \exp\left( 2\pi i a \vartheta^{xy}/p\right), \end{equation*}](http://www.ams.org/proc/2001-129-06/S0002-9939-00-05921-9/gif-abstract0/img1.gif)
where is of multiplicative order modulo the prime and and are arbitrary subsets of the residue ring modulo . In the special case , our bound is nontrivial for with any fixed , while if in addition we have it is nontrivial for . |