Question 99
Find all functions $f : \mathbb{Z} \to \mathbb{Z}$ such that
$$
f(f(a) + f(b)) = a + b - 1
$$
for all $a, b \in \mathbb{Z}$.
$$
f(f(a) + f(b)) = a + b - 1
$$
for all $a, b \in \mathbb{Z}$.
MathNet 2011 Question 99
Math Olympiad Vault · MathNet 2011