IMO 1979 LL USA65
Given f(x) \leqx for all real x and
IMO 1979 LL USA65
Origin: USA
Problem
Given f(x) \leqx for all real x and f(x + y) \leqf(x) + f(y) for all real x, y, prove that f(x) = x for all x.
Given f(x) \leqx for all real x and
Origin: USA
Given f(x) \leqx for all real x and f(x + y) \leqf(x) + f(y) for all real x, y, prove that f(x) = x for all x.