Symbolic transition systems separate data from process behaviour by a l l o wing the data to be uninstantiated. Designing a HML-like modal logic for these transition systems is interesting because of the subtle interplay b e t ween the quanti ers for the data and the modal operators (quanti ers on transitions). This paper presents the syntax and semantics of such a logic and discusses the design issues involved in its construction. The logic has been shown to be adequate with respect to strong

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... arly bisimulation over symbolic transition systems derived from Full LOTOS. We de ne what is meant by adequacy and discuss how we can reason about it with the aid of a mechanised theorem prover.