I-Sequences in the Category of Modules

The notion of I-sequences (introduced by Green) in the category of modules over finite-dimensional algebras is developed in this paper and particularly used to give an alternative proof for the results of Knörr concerning the existence and properties of relative projective covers in the category of modules over group algebras.     

Nonlinear functional boundary value problems involving the product of two nonlinearities

In this work, an existence theorem for the nonlinear quadratic two-point boundary value problems of functional differential equations is proved using a nonlinear alternative of Leray–Schauder type involving the product of two operators in Banach algebras. An example is also given to illustrate the abstract results presented here.     

On train algebras of rank 4

The existence of idempotent elements in train algebras of rank greater than 3 is an open question to be solved. Recent H. Guzzo results [7] on train algebras of rank 4 are based on the underlying assumption of the existence of an idempotent. In the present paper we establish the conditions that ensure the existence of such an idempotent. We also give additional properties on the Peirce decomposition which allow us to characterize some train algebras of rank 4. Finally, we give a characterization of the train algebras of rank 4 which are power-associative algebras or Jordan algebras.     

Cayley-dickson algebras and alternative loop algebras

In this paper we establish a relationship between alternative loop algebras and Cayley-Dickson algebras: any Cayley-Dickson algebra is a quotient algebra of an alternative loop algebra. Thus we give a new way of representing a Cayley-Dickson algebra. As an application, a result of Luiz G. X. de Barros is generalized.     

Cylindric algebras and finite polyadic algebras

In this survey paper the short history of cylindric and finitary polyadic algebras (term-definitionally equivalent to quasi-polyadic algebras) is sketched, and the two concepts are compared. Roughly speaking, finitary polyadic algebras constitute a subclass of cylindric algebras that include a transposition operator being strong enough. We discuss the following question: should the definition of cylindric algebras include a transposition operator? Results confirm that the existence of a transposition operator ensures representability (by relativised set algebras). The different variants of cylindric algebras including a transposition operator play an important role in the theory of cylindric-like algebras.     

Pfister involutions

The question of the existence of an analogue, in the framework of central simple algebras with involution, of the notion of Pfister form is raised. In particular, algebras with orthogonal involution which split as a tensor product of quaternion algebras with involution are studied. It is proven that, up to degree 16, over any extension over which the algebra splits, the involution is adjoint to a Pfister form. Moreover, cohomological invariants of those algebras with involution are discussed.     

Localization of Rota–Baxter algebras

A commutative Rota–Baxter algebra can be regarded as a commutative algebra that carries an abstraction of the integral operator. With the motivation of generalizing the study of algebraic geometry to Rota–Baxter algebras, we extend the central concept of localization for commutative algebras to commutative Rota–Baxter algebras. The existence of such a localization is proved and, under mild conditions, its explicit construction is obtained. The existence of tensor products of commutative Rota–Baxter algebras is also proved and the compatibility of localization and the tensor product of Rota–Baxter algebras is established. We further study Rota–Baxter coverings and show that they form a Grothendieck topology.     

Representation-finite derived tubular algebras

The use of quadratic forms as a tool for characterizing classes of algebras is well known and widely accepted. However, until now a characterization of the interesting class of derived tubular algebras, by properties of the (non-symmetric) Euler form only, failed because of the existence of so-called pg-critical algebras, whose Euler form manifest similar properties as those of tubular algebras. The present article fills this gap and provides a distinction between derived tubular algebras and derived pg-critical algebras. Furthermore, an explicit characterization of representation-finite derived tubular algebras in terms of their Euler forms will be given.     

Differential algebras of generalised functions with dense singularities

It is shown how chains of algebras of generalised functions may be used to construct algebras of generalised functions that are able to deal with larger classes of singularities than each of the constituent algebras in the chain. The general method is applied to a chain of almost everywhere algebras, yielding an algebra that can handle certain densely singular functions. The embedding of the distributions into the mentioned algebra, as well as the existence of solutions of nonlinear PDEs, is considered.     

An Alternative Definition of Quantifiers on Four-Valued Łukasiewicz Algebras

An alternative notion of an existential quantifier on four-valued ?ukasiewicz algebras is introduced. The class of four-valued ?ukasiewicz algebras endowed with this existential quantifier determines a variety which is denoted by \(\mathbb {M}_{\frac{2}{3}}\mathbb {L}_4\). It is shown that the alternative existential quantifier is interdefinable with the standard existential quantifier on a four-valued ?ukasiewicz algebra. Some connections between the new existential quantifier and the existential quantifiers defined on bounded distributive lattices and Boolean algebras are given. Finally, a completeness theorem for the monadic four-valued ?ukasiewicz predicate calculus corresponding to the dual of the alternative existential quantifier is proven.     

Calabi–Yau algebras and weighted quiver polyhedra

Dimer models have been used in string theory to construct path algebras with relations that are 3-dimensional Calabi–Yau Algebras. These constructions result in algebras that share some specific properties: they are finitely generated modules over their centers and their representation spaces are toric varieties. In order to describe these algebras we introduce the notion of a toric order and show that all toric orders which are 3-dimensional Calabi–Yau algebras can be constructed from dimer models on a torus. Toric orders are examples of a much broader class of algebras: positively graded cancellation algebras. For these algebras the CY-3 condition implies the existence of a weighted quiver polyhedron, which is an extension of dimer models obtained by replacing the torus with any two-dimensional compact orientable orbifold.     

Based algebras and standard bases for quasi-hereditary algebras

Quasi-hereditary algebras can be viewed as a Lie theory approach to the theory of finite dimensional algebras. Motivated by the existence of certain nice bases for representations of semisimple Lie algebras and algebraic groups, we will construct in this paper nice bases for (split) quasi-hereditary algebras and characterize them using these bases. We first introduce the notion of a standardly based algebra, which is a generalized version of a cellular algebra introduced by Graham and Lehrer, and discuss their representation theory. The main result is that an algebra over a commutative local noetherian ring with finite rank is split quasi-hereditary if and only if it is standardly full-based. As an application, we will give an elementary proof of the fact that split symmetric algebras are not quasi-hereditary unless they are semisimple. Finally, some relations between standardly based algebras and cellular algebras are also discussed.     

Comultiplications with Meson Algebras

The mesonic interior multipliciations have suggested the existence of mesonic comultiplications. The proof of their existence has motivated an intensive study of the meson algebra of an orthogonal sum, revealing its twisted gradations and its canonical projectors. The traditional applications of comultiplications follow. A final application to mesonic deformations corroborates the close relationship between Clifford algebras and meson algebras.     

Graded alphabets,circular codes,free Lie algebras and comma-free codes

We show how the use of graded alphabets allows one to provide simpler proofs of some results on free monoids and free Lie algebras. We first generalize to graded alphabets the characterization of the length distributions of circular codes. We also show that the existence of a circular code with a given distribution of degrees is equivalent to the existence of an embedding of Lie algebras. We finally give a generalization to graded alphabets of the famous result of Eastman on comma free codes of odd degree.     

Derivations of noncommutative Arens algebras

The present paper deals with derivations of noncommutative Arens algebras. We prove that every derivation of an Arens algebra associated with a von Neumann algebra and a faithful normal finite trace is inner. In particular, each derivation on such algebras is automatically continuous in the natural topology, and in the commutative case, even for semi-finite traces, all derivations are identically zero. At the same time, the existence of noninner derivations is proved for noncommutative Arens algebras with a semi-finite but nonfinite trace.     

Anosov Lie algebras and algebraic units in number fields

We study nilmanifolds admitting Anosov automorphisms by applying elementary properties of algebraic units in number fields to the associated Anosov Lie algebras. We identify obstructions to the existence of Anosov Lie algebras. The case of 13-dimensional Anosov Lie algebras is worked out as an illustration of the technique. Also, we recapture the following known results: (1) Every 7-dimensional Anosov nilmanifold is toral, and (2) every 8-dimensional Anosov Lie algebra with 3 or 5-dimensional derived algebra contains an abelian factor.     

Equations des algèbres Lie triple qui sont des algèbres train

In this paper, we consider equations of Lie triple algebras that are train algebras. We obtain two different types of equations depending on assuming the existence of an idempotent or a pseudo-idempotent.In general Lie triple algebras are not power-associative. However we show that their train equation with an idempotent is similar to train equations of power-associative algebras that are train algebras and we prove that Lie triple algebras that are train algebras of rank $\le 4$ with an idempotent are Jordan algebras.Moreover, the set of non-trivial idempotents has the same expression in Peirce decomposition as that of $e$-stable power-associative algebras.We also prove that the algebra obtained by $2$-gametization process of a Lie triple algebra is a Lie triple one.     

Existentially closed structures and some embedding theorems

Mathematical Notes - Using the notion of an existentially closed structure, we obtain embedding theorems for groups and Lie algebras. We also prove the existence of certain groups and Lie algebras...     

Topo-canonical completions of closure algebras and Heyting algebras

We introduce and investigate topo-canonical completions of closure algebras and Heyting algebras. We develop a duality theory that is an alternative to Esakia’s duality, describe duals of topo-canonical completions in terms of the Salbany and Banaschewski compactifications, and characterize topo-canonical varieties of closure algebras and Heyting algebras. Consequently, we show that ideal completions preserve no identities of Heyting algebras. We also characterize definable classes of topological spaces. Received January 20, 2006; accepted in final form September 12, 2006.     

Solvable Lie algebras are not that hypo

We study a type of left-invariant structure on Lie groups or, equivalently, on Lie algebras. We introduce obstructions to the existence of a hypo structure, namely the five-dimensional geometry of hypersurfaces in manifolds with holonomy SU(3). The choice of a splitting \mathfrakg^* = V₁ ?V₂ {\mathfrak{g}^*} = {V_1} \oplus {V_2} , and the vanishing of certain associated cohomology groups, determine a first obstruction. We also construct necessary conditions for the existence of a hypo structure with a fixed almost-contact form. For nonunimodular Lie algebras, we derive an obstruction to the existence of a hypo structure, with no choice involved. We apply these methods to classify solvable Lie algebras that admit a hypo structure.