Problem

Source: 2015 Saudi Arabia BMO TST II p1

Tags: algebra, functional equation, functional, function, Increasing



Find all strictly increasing functions $f : Z \to R$ such that for any $m, n \in Z$ there exists a $k \in Z$ such that $f(k) = f(m) - f(n)$. Nguyễn Duy Thái Sơn