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The notions of bisimulation and simulation are used for graph reduction and are widely employed in many areas: modal logic, concurrency theory, set theory, formal verification, and so forth. In particular, in the context of formal verification they are used to tackle the so-called state-explosion problem. The faster algorithms to compute the maximum(More)
In this paper we consider the relative expressive power of two very common operators applicable to sets and multisets: the with and the union operators. For such operators we prove that they are not mutually expressible by means of existentially quantiied formulae. In order to prove our results, canonical forms for set-theoretic and multiset-theoretic(More)
We present an algorithm that computes in a linear number of symbolic steps (<i>O</i>(&verbar;<i>V</i>&verbar;)) the strongly connected components (sccs) of a graph <i>G</i> = &lang;<i>V, E</i>&rang; represented by an Ordered Binary Decision Diagram (OBDD). This result matches the complexity of the (celebrated) Tarjan's algorithm operating on explicit data(More)
In this paper we present a study of the problem of handling constraints made by conjunctions of positive and negative literals based on the predicate symbols =, <inline-equation> <f> &#8712;,<hsp sp="0.265">&#8746;</f> </inline-equation> and <inline-equation> <f> &dvbm0;</f> </inline-equation> (i.e., disjointness of two sets) in a (hybrid) universe of <?Pub(More)
Information flow security properties such as noninterference ensure the protection of confidential data by strongly limiting the flow of sensitive information. However, to deal with real applications, it is often necessary to admit mechanisms for downgrading or declassifying information. In this paper, we propose a general unwinding framework for(More)
We propose an efficient algorithmic solution to the problem of determining a Bisimulation Relation on a finite structure working both on the explicit and on the implicit (symbolic) representation. As far as the explicit case is concerned, starting from a set-theoretic point of view we propose an algorithm that optimizes the solution to the Relational(More)