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Many formal models for in nite-state concurrent systems are equivalent to special classes of rewrite systems. We classify these models by their expressiveness and de ne a hierarchy of classes of rewrite systems. We show that this hierarchy is strict with respect to bisimulation equivalence. The most general and most expressive class of systems in this(More)
We introduce Higher-Order Rewrite Systems (HRS) which extend term rewriting to-terms. HRS can describe computations on arbitrary terms with bound variables. We show that rewriting is closely related to undirected equational reasoning , and extend three connuence results from term rewriting to HRS: the critical pair lemma by Knuth and Bendix, connuence of(More)
Department of Computer Science, University of Edinburgh, JCMB, Edinburgh EH9 3JZ, UK. e-mail: mayrri@dcs.ed.ac.uk Abstract. Lossy counter machines are defined as Minsky n-counter machines where the values in the counters can spontaneously decrease at any time. While termination is decidable for lossy counter machines, structural termination (termination for(More)
We consider the model checking problem for probabilistic pushdown automata (pPDA) and properties expressible in various probabilistic logics. We start with properties that can be formulated as instances of a generalized random walk problem. We prove that both qualitative and quantitative model checking for this class of properties and pPDA is decidable.(More)
We describe a new and more efficient algorithm for checking universality and language inclusion on nondeterministic finite word automata (NFA) and tree automata (TA). To the best of our knowledge, the antichain-based approach proposed by De Wulf et al. was the most efficient one so far. Our idea is to exploit a simulation relation on the states of finite(More)
We consider Dense-Timed Petri Nets (TPN), an extension of Petri nets in which each token is equipped with a real-valued clock and where the semantics is lazy (i.e., enabled transitions need not fire; time can pass and disable transitions). We consider the following verification problems for TPNs. (i) Zenoness: whether there exists a zeno-computation from a(More)
We show that checking weak bisimulation equivalence of two context-free processes (also called BPA-processes) is EXPTIME-hard, even under the condition that the processes are normed. Furthermore, checking weak regularity (finiteness up to weak bisimilarity) for context-free processes is EXPTIME-hard as well.Adding a finite control of the minimal non-trivial(More)