# Quelques contributions en logique mathématique et en théorie des automates

Abstract : This work deals mainly with automata theory, mathematical logic and their applications. In the first part, we use finite automata to prove the automaticity of several logical structures over finite words written in a countable infinite alphabet. These structures involve predicates like $pred$, $clone$ and $diff$, where $x pred y$ holds if $x$ is a strict prefix of $y$, $clone(x)$ holds when the two last letters of $x$ are equal, and $diff(x)$ holds when all letters of $x$ are pairwise distinct. The automaticity results allow to deduce the decidability of logical theories associated with these structures. Other related decidability/undecidability results are obtained by logical interpretation. In the second part, we generalize the concept of Common Follow Sets of a regular expression to homogeneous finite automata. Based on this concept and a particular class of binary trees, we devise an efficient algorithm to reduce/minimize the number of transitions of triangular automata. On the one hand, we prove that the produced reduced automaton is asymptotically minimal, in the sense that for an automaton with $n$ states, the number of transitions in the reduced automaton is equivalent to $n(log_2 n)^2$ , which corresponds at the same time to the upper and the lower known bounds. On the other hand, experiments reveal that for small values of $n$, all minimal automata are exactly those obtained by our reduction, which lead us to conjecture that our construction is not only a reduction but a minimization. In the last part, we present an experimental study on the use of special automata on partial words for the approximate pattern matching problem in dictionaries. Despite exponential theoretical time and space upper bounds, our experiments show that, in many practical cases, these automata have a linear size and allow a linear search time
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https://tel.archives-ouvertes.fr/tel-01328133
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### Citation

Mohamed Dahmoune. Quelques contributions en logique mathématique et en théorie des automates. Mathématiques générales [math.GM]. Université Paris-Est, 2014. Français. ⟨NNT : 2014PEST1013⟩. ⟨tel-01328133⟩

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