A Crevice on the Crane Beach: Finite-Degree Predicates

First-order logic (FO) over words is shown to be equiexpressive with FO equipped with a restricted set of numerical predicates, namely the order, a binary predicate MSB$_0$, and the finite-degree predicates: FO[Arb] = FO[<, MSB$_0$, Fin]. The Crane Beach Property (CBP), introduced more than a decade ago, is true of a logic if all the expressible languages admitting a neutral letter are regular. Although it is known that FO[Arb] does not have the CBP, it is shown here that the (strong form of the) CBP holds for both FO[<, Fin] and FO[<, MSB$_0$]. Thus FO[<, Fin] exhibits a form of locality and the CBP, and can still express a wide variety of languages, while being one simple predicate away from the expressive power of FO[Arb]. The counting ability of FO[<, Fin] is studied as an application.Comment: Submitte

Continuity of Functional Transducers: A Profinite Study of Rational Functions

A word-to-word function is continuous for a class of languages~$\mathcal{V}$ if its inverse maps $\mathcal{V}$_languages to~$\mathcal{V}$. This notion provides a basis for an algebraic study of transducers, and was integral to the characterization of the sequential transducers computable in some circuit complexity classes. Here, we report on the decidability of continuity for functional transducers and some standard classes of regular languages. To this end, we develop a robust theory rooted in the standard profinite analysis of regular languages. Since previous algebraic studies of transducers have focused on the sole structure of the underlying input automaton, we also compare the two algebraic approaches. We focus on two questions: When are the automaton structure and the continuity properties related, and when does continuity propagate to superclasses

Automates à contraintes semilinéaires = Automata with a semilinear constraint

Cette thèse présente une étude dans divers domaines de l'informatique théorique de modèles de calculs combinant automates finis et contraintes arithmétiques. Nous nous intéressons aux questions de décidabilité, d'expressivité et de clôture, tout en ouvrant l'étude à la complexité, la logique, l'algèbre et aux applications. Cette étude est présentée au travers de quatre articles de recherche. Le premier article, Affine Parikh Automata, poursuit l'étude de Klaedtke et Ruess des automates de Parikh et en définit des généralisations et restrictions. L'automate de Parikh est un point de départ de cette thèse; nous montrons que ce modèle de calcul est équivalent à l'automate contraint que nous définissons comme un automate qui n'accepte un mot que si le nombre de fois que chaque transition est empruntée répond à une contrainte arithmétique. Ce modèle est naturellement étendu à l'automate de Parikh affine qui effectue une opération affine sur un ensemble de registres lors du franchissement d'une transition. Nous étudions aussi l'automate de Parikh sur lettres: un automate qui n'accepte un mot que si le nombre de fois que chaque lettre y apparaît répond à une contrainte arithmétique. Le deuxième article, Bounded Parikh Automata, étudie les langages bornés des automates de Parikh. Un langage est borné s'il existe des mots w_1, w_2, ..., w_k tels que chaque mot du langage peut s'écrire w_1...w_1w_2...w_2...w_k...w_k. Ces langages sont importants dans des domaines applicatifs et présentent usuellement de bonnes propriétés théoriques. Nous montrons que dans le contexte des langages bornés, le déterminisme n'influence pas l'expressivité des automates de Parikh. Le troisième article, Unambiguous Constrained Automata, introduit les automates contraints non ambigus, c'est-à-dire pour lesquels il n'existe qu'un chemin acceptant par mot reconnu par l'automate. Nous montrons qu'il s'agit d'un modèle combinant une meilleure expressivité et de meilleures propriétés de clôture que l'automate contraint déterministe. Le problème de déterminer si le langage d'un automate contraint non ambigu est régulier est montré décidable. Le quatrième article, Algebra and Complexity Meet Contrained Automata, présente une étude des représentations algébriques qu'admettent les automates contraints et les automates de Parikh affines. Nous déduisons de ces caractérisations des résultats d'expressivité et de complexité. Nous montrons aussi que certaines hypothèses classiques en complexité computationelle sont reliées à des résultats de séparation et de non clôture dans les automates de Parikh affines. La thèse est conclue par une ouverture à un possible approfondissement, au travers d'un certain nombre de problèmes ouverts.This thesis presents a study from the theoretical computer science perspective of computing models combining finite automata and arithmetic constraints. We focus on decidability questions, expressiveness, and closure properties, while opening the study to complexity, logic, algebra, and applications. This thesis is presented through four research articles. The first article, Affine Parikh Automata, continues the study of Klaedtke and Ruess on Parikh automata and defines generalizations and restrictions of this model. The Parikh automaton is one of the starting points of this thesis. We show that this model of computation is equivalent to the constrained automaton that we define as an automaton which accepts a word only if the number of times each transition is taken satisfies a given arithmetic constraint. This model is naturally extended to affine Parikh automata, in which an affine transformation is applied to a set of registers on taking a transition. We also study the Parikh automaton on letters, that is, an automaton which accepts a word only if the number of times each letter appears in the word verifies an arithmetic constraint. The second article, Bounded Parikh Automata, focuses on the bounded languages of Parikh automata. A language is bounded if there are words w_1, w_2, ..., w_k such that every word in the language can be written as w_1...w_1w_2...w_2 ... w_k...w_k. These languages are important in applications and usually display good theoretical properties. We show that, over the bounded languages, determinism does not influence the expressiveness of Parikh automata. The third article, Unambiguous Constrained Automata, introduces the concept of unambiguity in constrained automata. An automaton is unambiguous if there is only one accepting path per word of its language. We show that the unambiguous constrained automaton is an appealing model of computation which combines a better expressiveness and better closure properties than the deterministic constrained automaton. We show that it is decidable whether the language of an unambiguous constrained automaton is regular. The fourth article, Algebra and Complexity Meet Constrained Automata, presents a study of algebraic representations of constrained automata and affine Parikh automata. We deduce expressiveness and complexity results from these characterizations. We also study how classical computational complexity hypotheses help in showing separations and nonclosure properties in affine Parikh automata. The thesis is concluded by a presentation of possible future avenues of research, through several open problems

Bounded Parikh Automata

The Parikh finite word automaton model (PA) was introduced and studied by Klaedtke and Ruess in 2003. Here, by means of related models, it is shown that the bounded languages recognized by PA are the same as those recognized by deterministic PA. Moreover, this class of languages is the class of bounded languages whose set of iterations is semilinear.Comment: In Proceedings WORDS 2011, arXiv:1108.341

Weak Cost Register Automata are Still Powerful

We consider one of the weakest variants of cost register automata over a tropical semiring, namely copyless cost register automata over $\mathbb{N}$ with updates using $\min$ and increments. We show that this model can simulate, in some sense, the runs of counter machines with zero-tests. We deduce that a number of problems pertaining to that model are undecidable, in particular equivalence, disproving a conjecture of Alur et al. from 2012. To emphasize how weak these machines are, we also show that they can be expressed as a restricted form of linearly-ambiguous weighted automata.Comment: 16 page

EXTREMELY UNIFORM BRANCHING PROGRAMS

We propose a new descriptive complexity notion of uniformity for branching programs solving problems defined on structured data. We observe that FO[=]-uniform (n-way) branching programs are unable to solve the tree evaluation problem studied by Cook, McKenzie, Wehr, Braverman and Santhanam [8] because such programs possess a variant of their thriftiness property. Similarly, FO[=]-uniform (n-way) branching programs are unable to solve the P-complete GEN problem because such programs possess the incremental property studied by Gál, Kouck´y and McKenzie [10]. 1

On polynomial recursive sequences

International audienceWe study the expressive power of polynomial recursive sequences, a nonlinear extension of the well-known class of linear recursive sequences. These sequences arise naturally in the study of nonlinear extensions of weighted automata, where (non)expressiveness results translate to class separations. A typical example of a polynomial recursive sequence is $b_n=n!$. Our main result is that the sequence $u_n=n^n$ is not polynomial recursive