  We prove an analogue of Fekete's subadditivity lemma for functions of several
real variables which are subadditive in each variable taken singularly. This
extends both the classical case for subadditive functions of one real variable,
and a result in a previous paper by the author. While doing so, we prove that
the functions with the property mentioned above are bounded in every closed and
bounded subset of their domain. The arguments follows those of Chapter 6 in E.
Hille's 1948 textbook.
