Em. Stein et S. Wainger, Discrete analogues in harmonic analysis - I: l(2) estimates for singular radon transforms, AM J MATH, 121(6), 1999, pp. 1291-1336
This paper studies the discrete analogues of singular Radon transforms. We
prove the l(2) boundedness for those operators that are "quasi-translation-
invariant" The approach used is related to the "circle-method" of Hardy and
Littlewood, and requires multi-dimensional extensions of Weyl sums and Gau
ss sums, as well as variants that replace scalar sums by operator sums.