“…Banks, Heath-Brown and Shparlinski [1] have considered the average over a and proved that for any ε > 0 there exists some δ > 0 such that for a sufficiently large X 1≤a≤q gcd(a,q)=1 |E(X; q, a)| ≤ X 1−δ holds uniformly for q < X 1−ε . For other examples, see [2,4,6,7,15].…”