  In this paper we prove in a rigorous mathematical way (using the Clifford
bundle formalism) that the energies and momenta of two distinct and arbitrary
free Maxwell fields (of finite energies and momenta) that are superposed are
additive and thus that there is no incompatibility between the principle of
superposition of fields and the principle of energy-momentum conservation,
contrary to some recent claims. Our proof depends on a noticeable formula for
the energy-momentum 1-form fields T^{a},namely Riesz formula, which is valid
for any electromagnetic field configuration F satisfying Maxwell equation.
