Question 3
Find all functions $f$ from the set $\{\mathbf{R}\}$ of real numbers into $\{\mathbf{R}\}$ which satisfy for all $x, y, z \in \{\mathbf{R}\}$ the identity
$$
f(f(x)+f(y)+f(z))=f(f(x)-f(y))+f(2 x y+f(z))+2 f(x z-y z)
$$
$$
f(f(x)+f(y)+f(z))=f(f(x)-f(y))+f(2 x y+f(z))+2 f(x z-y z)
$$