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A conjecture on the concatenation product

Jean-Eric Pin, Pascal Weil (2010)

RAIRO - Theoretical Informatics and Applications

In a previous paper, the authors studied the polynomial closure of a variety of languages and gave an algebraic counterpart, in terms of Mal'cev products, of this operation. They also formulated a conjecture about the algebraic counterpart of the boolean closure of the polynomial closure – this operation corresponds to passing to the upper level in any concatenation hierarchy. Although this conjecture is probably true in some particular cases, we give a counterexample in the general case....

A Game Theoretical Approach to The Algebraic Counterpart of The Wagner Hierarchy : Part II

Jérémie Cabessa, Jacques Duparc (2009)

RAIRO - Theoretical Informatics and Applications

The algebraic counterpart of the Wagner hierarchy consists of a well-founded and decidable classification of finite pointed ω-semigroups of width 2 and height ωω. This paper completes the description of this algebraic hierarchy. We first give a purely algebraic decidability procedure of this partial ordering by introducing a graph representation of finite pointed ω-semigroups allowing to compute their precise Wagner degrees. The Wagner degree of any ω-rational language can therefore be computed...

A game theoretical approach to the algebraic counterpart of the Wagner hierarchy : Part I

Jérémie Cabessa, Jacques Duparc (2009)

RAIRO - Theoretical Informatics and Applications

The algebraic study of formal languages shows that ω-rational sets correspond precisely to the ω-languages recognizable by finite ω-semigroups. Within this framework, we provide a construction of the algebraic counterpart of the Wagner hierarchy. We adopt a hierarchical game approach, by translating the Wadge theory from the ω-rational language to the ω-semigroup context. More precisely, we first show that the Wagner degree is indeed a syntactic invariant. We then define a reduction relation on...

A Garside presentation for Artin-Tits groups of type C ˜ n

F. Digne (2012)

Annales de l’institut Fourier

We prove that an Artin-Tits group of type C ˜ is the group of fractions of a Garside monoid, analogous to the known dual monoids associated with Artin-Tits groups of spherical type and obtained by the “generated group” method. This answers, in this particular case, a general question on Artin-Tits groups, gives a new presentation of an Artin-Tits group of type C ˜ , and has consequences for the word problem, the computation of some centralizers or the triviality of the center. A key point of the proof...

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