Prove:

Proof. By definition

Applying the law for complex numbers that states

we get

Now using the law that states

            |z₁, z₂, ... ,z_n | = |z₁||z₂| ..... |z_n|

we get

From 2) and 3) we have

As n , this yields a corresponding inequality for the integrals that are the limits of the respective sums: