Question 16
Let $\mathbb{Z}$ be the set of integer numbers. Determine all functions $f : \mathbb{Z} \to \mathbb{Z}$
such that
$$
f(x + f(y + 1)) + f(xy) = f(x + 1)(f(y) + 1)
$$
for any integers $x, y$.
such that
$$
f(x + f(y + 1)) + f(xy) = f(x + 1)(f(y) + 1)
$$
for any integers $x, y$.