  In this paper we present a new formulation of the Beurling-Malliavin density
(Proposition 1). Then we consider the upper Polya density and show how its
existence is connected with the concept of subadditivity; moreover, by means of
some quantities introduced for proving Proposition 1, a theorem is presented
that clarifies the connection between the upper Polya and the
Beurling-Malliavin densities. In the last section we discuss the classical
definition of the upper Polya density and we prove a result which seems to be
new.
