  In this note we consider the problem of introducing variables in temporal
logic programs under the formalism of "Temporal Equilibrium Logic" (TEL), an
extension of Answer Set Programming (ASP) for dealing with linear-time modal
operators. To this aim, we provide a definition of a first-order version of TEL
that shares the syntax of first-order Linear-time Temporal Logic (LTL) but has
a different semantics, selecting some LTL models we call "temporal stable
models". Then, we consider a subclass of theories (called "splittable temporal
logic programs") that are close to usual logic programs but allowing a
restricted use of temporal operators. In this setting, we provide a syntactic
definition of "safe variables" that suffices to show the property of "domain
independence" -- that is, addition of arbitrary elements in the universe does
not vary the set of temporal stable models. Finally, we present a method for
computing the derivable facts by constructing a non-temporal logic program with
variables that is fed to a standard ASP grounder. The information provided by
the grounder is then used to generate a subset of ground temporal rules which
is equivalent to (and generally smaller than) the full program instantiation.
