Almost periodic functions and property of universality of Dirichlet L-functions

The term "universality" for functions was introduced in the early 1970s by E.M. Voronin and the meaning that is embedded in this concept is that a very general class of analytic functions admits approximation by vertical shifts of a given function. In 1975, S.M. Voronin proved the universality property for Riemann zeta-functions, and in 1977 for the Dirichlet L-function.
In this paper we propose a proof of the universality property for Dirichlet L-functions that is different from SM's proof. Voronin, based on a rapid approximation in the critical band of Dirichlet L-functions by Dirichlet polynomials.