  This note states and proves an integral representation formula of the
``variation-of-constant'' type for continuous solutions of linear
non-autonomous difference delay systems, in terms of a Lebesgue-Stieltjes
integral involving a fundamental solution and the initial data of the system.
This gives a precise and correct version of several formulations appearing in
the literature, and extends them to the time-varying case. This is of
importance for further stability studies of various kinds of delay systems.
