Question 26
Let $\mathbb{R}$ denote the set of real numbers. Find all functions $f: \mathbb{R} \to \mathbb{R}$ such that
$$
x f(f(y)) + y f(y - x) = f(f(x + y) - x) f(y)
$$
for all $x, y \in \mathbb{R}$.
$$
x f(f(y)) + y f(y - x) = f(f(x + y) - x) f(y)
$$
for all $x, y \in \mathbb{R}$.