EN
For positive integers m and N, we estimate the rational exponential sums with denominator m over the reductions modulo m of elements of the set
ℱ(N) = {s/r : r,s ∈ ℤ, gcd(r,s) = 1, N ≥ r > s ≥ 1}
of Farey fractions of order N (only fractions s/r with gcd(r,m) = 1 are considered).