163 research outputs found
On a Definition of a Variety of Monadic ℓ-Groups
In this paper we expand previous results obtained in [2] about the study of categorical equivalence between the category IRL 0 of integral residuated lattices with bottom, which generalize MV-algebras and a category whose objects are called c-differential residuated lattices. The equivalence is given by a functor K∙, motivated by an old construction due to J. Kalman, which was studied by Cignoli in [3] in the context of Heyting and Nelson algebras. These results are then specialized to the case of MV-algebras and the corresponding category MV∙ of monadic MV-algebras induced by “Kalman’s functor” K∙. Moreover, we extend the construction to ℓ-groups introducing the new category of monadic ℓ-groups together with a functor Γ♯, that is “parallel” to the well known functor Γ between ℓ and MV-algebras.Facultad de Ciencias Exacta
Stone duality above dimension zero: Axiomatising the algebraic theory of C(X)
It has been known since the work of Duskin and Pelletier four decades ago
that KH^op, the category opposite to compact Hausdorff spaces and continuous
maps, is monadic over the category of sets. It follows that KH^op is equivalent
to a possibly infinitary variety of algebras V in the sense of Slominski and
Linton. Isbell showed in 1982 that the Lawvere-Linton algebraic theory of V can
be generated using a finite number of finitary operations, together with a
single operation of countably infinite arity. In 1983, Banaschewski and Rosicky
independently proved a conjecture of Bankston, establishing a strong negative
result on the axiomatisability of KH^op. In particular, V is not a finitary
variety--Isbell's result is best possible. The problem of axiomatising V by
equations has remained open. Using the theory of Chang's MV-algebras as a key
tool, along with Isbell's fundamental insight on the semantic nature of the
infinitary operation, we provide a finite axiomatisation of V.Comment: 26 pages. Presentation improve
Algebraic deformations of toric varieties II. Noncommutative instantons
We continue our study of the noncommutative algebraic and differential
geometry of a particular class of deformations of toric varieties, focusing on
aspects pertinent to the construction and enumeration of noncommutative
instantons on these varieties. We develop a noncommutative version of twistor
theory, which introduces a new example of a noncommutative four-sphere. We
develop a braided version of the ADHM construction and show that it
parametrizes a certain moduli space of framed torsion free sheaves on a
noncommutative projective plane. We use these constructions to explicitly build
instanton gauge bundles with canonical connections on the noncommutative
four-sphere that satisfy appropriate anti-selfduality equations. We construct
projective moduli spaces for the torsion free sheaves and demonstrate that they
are smooth. We define equivariant partition functions of these moduli spaces,
finding that they coincide with the usual instanton partition functions for
supersymmetric gauge theories on C^2.Comment: 62 pages; v2: typos corrected, references updated; Final version to
be published in Advances in Theoretical and Mathematical Physic
Stacks of group representations
We start with a small paradigm shift about group representations, namely the
observation that restriction to a subgroup can be understood as an
extension-of-scalars. We deduce that, given a group , the derived and the
stable categories of representations of a subgroup can be constructed out
of the corresponding category for by a purely triangulated-categorical
construction, analogous to \'etale extension in algebraic geometry.
In the case of finite groups, we then use descent methods to investigate when
modular representations of the subgroup can be extended to . We show
that the presheaves of plain, derived and stable representations all form
stacks on the category of finite -sets (or the orbit category of ), with
respect to a suitable Grothendieck topology that we call the sipp topology.
When contains a Sylow subgroup of , we use sipp Cech cohomology to
describe the kernel and the image of the homomorphism , where
denotes the group of endotrivial representations.Comment: Slightly revised version of the 2012 June 21 versio
Algebraic recognizability of regular tree languages
We propose a new algebraic framework to discuss and classify recognizable
tree languages, and to characterize interesting classes of such languages. Our
algebraic tool, called preclones, encompasses the classical notion of syntactic
Sigma-algebra or minimal tree automaton, but adds new expressivity to it. The
main result in this paper is a variety theorem \`{a} la Eilenberg, but we also
discuss important examples of logically defined classes of recognizable tree
languages, whose characterization and decidability was established in recent
papers (by Benedikt and S\'{e}goufin, and by Bojanczyk and Walukiewicz) and can
be naturally formulated in terms of pseudovarieties of preclones. Finally, this
paper constitutes the foundation for another paper by the same authors, where
first-order definable tree languages receive an algebraic characterization
Deformation Theory and Partition Lie Algebras
A theorem of Lurie and Pridham establishes a correspondence between formal
moduli problems and differential graded Lie algebras in characteristic zero,
thereby formalising a well-known principle in deformation theory. We introduce
a variant of differential graded Lie algebras, called partition Lie algebras,
in arbitrary characteristic. We then explicitly compute the homotopy groups of
free algebras, which parametrise operations. Finally, we prove generalisations
of the Lurie-Pridham correspondence classifying formal moduli problems via
partition Lie algebras over an arbitrary field, as well as over a complete
local base.Comment: 89 page
Adding modular predicates to first-order fragments
We investigate the decidability of the definability problem for fragments of
first order logic over finite words enriched with modular predicates. Our
approach aims toward the most generic statements that we could achieve, which
successfully covers the quantifier alternation hierarchy of first order logic
and some of its fragments. We obtain that deciding this problem for each level
of the alternation hierarchy of both first order logic and its two-variable
fragment when equipped with all regular numerical predicates is not harder than
deciding it for the corresponding level equipped with only the linear order and
the successor. For two-variable fragments we also treat the case of the
signature containing only the order and modular predicates.Relying on some
recent results, this proves the decidability for each level of the alternation
hierarchy of the two-variable first order fragmentwhile in the case of the
first order logic the question remains open for levels greater than two.The
main ingredients of the proofs are syntactic transformations of first order
formulas as well as the algebraic framework of finite categories
Silent Transitions in Automata with Storage
We consider the computational power of silent transitions in one-way automata
with storage. Specifically, we ask which storage mechanisms admit a
transformation of a given automaton into one that accepts the same language and
reads at least one input symbol in each step.
We study this question using the model of valence automata. Here, a finite
automaton is equipped with a storage mechanism that is given by a monoid.
This work presents generalizations of known results on silent transitions.
For two classes of monoids, it provides characterizations of those monoids that
allow the removal of \lambda-transitions. Both classes are defined by graph
products of copies of the bicyclic monoid and the group of integers. The first
class contains pushdown storages as well as the blind counters while the second
class contains the blind and the partially blind counters.Comment: 32 pages, submitte
Iteration Algebras for UnQL Graphs and Completeness for Bisimulation
This paper shows an application of Bloom and Esik's iteration algebras to
model graph data in a graph database query language. About twenty years ago,
Buneman et al. developed a graph database query language UnQL on the top of a
functional meta-language UnCAL for describing and manipulating graphs.
Recently, the functional programming community has shown renewed interest in
UnCAL, because it provides an efficient graph transformation language which is
useful for various applications, such as bidirectional computation. However, no
mathematical semantics of UnQL/UnCAL graphs has been developed. In this paper,
we give an equational axiomatisation and algebraic semantics of UnCAL graphs.
The main result of this paper is to prove that completeness of our equational
axioms for UnCAL for the original bisimulation of UnCAL graphs via iteration
algebras. Another benefit of algebraic semantics is a clean characterisation of
structural recursion on graphs using free iteration algebra.Comment: In Proceedings FICS 2015, arXiv:1509.0282
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