  The cost of LTL model checking is highly sensitive to the length of the
formula under verification. We observe that, under some specific conditions,
the input LTL formula can be reduced to an easier-to-handle one before model
checking. In our reduction, these two formulae need not to be logically
equivalent, but they share the same counterexample set w.r.t the model. In the
case that the model is symbolically represented, the condition enabling such
reduction can be detected with a lightweight effort (e.g., with SAT-solving).
In this paper, we tentatively name such technique "Counterexample-Preserving
Reduction" (CePRe for short), and finally the proposed technquie is
experimentally evaluated by adapting NuSMV.
