Suppose that function f : R → R satisfies the inequality:

n

| ∑ 3^r{f(x + ry) - f(x - ry)}| ≤ 1 for every positive integer r, http://upload.wikimedia.org/math/e/2...7521a7e732.png x, y http://upload.wikimedia.org/math/7/b...e1a4c7cff0.png http://upload.wikimedia.org/math/5/9...610685c9f7.png

r = 1

Prove that f(x) = constant