Carla Piazza

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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 propose an efficient algorithmic solution to the problem of determining a Bisimulation Relation on a finite structure. Starting from a set-theoretic point of view we propose an algorithm that optimizes the solution to the Relational coarsest Partition problem given by Paige and Tarjan in 1987 and its use in model-checking packages is(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)
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 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 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 quantified formulae. In order to prove our results, canonical forms for set-theoretic and multiset-theoretic(More)
Many biological systems can be modeled using systems of ordinary differential algebraic equations (e.g., S-systems), thus allowing the study of their solutions and behavior automatically with suitable software tools (e.g., PLAS, Octave/Matlab). Usually, numerical solutions (traces or trajectories) for appropriate initial conditions are analyzed in order to(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)
In this paper, we suggest a possible confluence of the theory of hybrid automata and the techniques of algorithmic algebra to create a computational basis for systems biology. We describe a method to compute bounded reachability by combining Taylor polynomials and cylindric algebraic decomposition algorithms. We discuss the power and limitations of the(More)