  By using nonstandard analysis, we prove embeddability properties of
difference sets $A-B$ of sets of integers. (A set $A$ is "embeddable" into $B$
if every finite configuration of $A$ has shifted copies in $B$.) As corollaries
of our main theorem, we obtain improvements of results by I.Z. Ruzsa about
intersections of difference sets, and of Jin's theorem (as refined by V.
Bergelson, H. F\"urstenberg and B. Weiss), where a precise bound is given on
the number of shifts of $A-B$ which are needed to cover arbitrarily large
intervals.
