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Power-cancellation of CW-complexes with few cells.

Irene Llerena (1992)

Publicacions Matemàtiques

In this paper we use the fact that the rings of integer matrices have the power-substitution property in order to obtain a power-cancellation property for homotopy types of CW-complexes with one cell in dimensions 0 and 4n and a finite number of cells in dimension 2n.

Precovers

Ladislav Bican, Blas Torrecillas (2003)

Czechoslovak Mathematical Journal

Let 𝒢 be an abstract class (closed under isomorpic copies) of left R -modules. In the first part of the paper some sufficient conditions under which 𝒢 is a precover class are given. The next section studies the 𝒢 -precovers which are 𝒢 -covers. In the final part the results obtained are applied to the hereditary torsion theories on the category on left R -modules. Especially, several sufficient conditions for the existence of σ -torsionfree and σ -torsionfree σ -injective covers are presented.

Precovers and Goldie’s torsion theory

Ladislav Bican (2003)

Mathematica Bohemica

Recently, Rim and Teply , using the notion of τ -exact modules, found a necessary condition for the existence of τ -torsionfree covers with respect to a given hereditary torsion theory τ for the category R -mod of all unitary left R -modules over an associative ring R with identity. Some relations between τ -torsionfree and τ -exact covers have been investigated in . The purpose of this note is to show that if σ = ( 𝒯 σ , ℱ σ ) is Goldie’s torsion theory and ℱ σ is a precover class, then ℱ τ is a precover class whenever...

Preradicals

Ladislav Bican, Pavel Jambor, Tomáš Kepka, Petr Němec (1974)

Commentationes Mathematicae Universitatis Carolinae

Prescribing endomorphism algebras of ℵ n -free modules

Rüdiger Göbel, Daniel Herden, Saharon Shelah (2014)

Journal of the European Mathematical Society

It is a well-known fact that modules over a commutative ring in general cannot be classified, and it is also well-known that we have to impose severe restrictions on either the ring or on the class of modules to solve this problem. One of the restrictions on the modules comes from freeness assumptions which have been intensively studied in recent decades. Two interesting, distinct but typical examples are the papers by Blass [1] and Eklof [8], both jointly with Shelah. In the first case the authors...

Présentation jordanienne de l'algèbre de Weyl A₂

J. Alev, F. Dumas (2001)

Annales Polonici Mathematici

Let k be a commutative field. For any a,b∈ k, we denote by J a , b ( k ) the deformation of the 2-dimensional Weyl algebra over k associated with the Jordanian Hecke symmetry with parameters a and b. We prove that: (i) any J a , b ( k ) can be embedded in the usual Weyl algebra A₂(k), and (ii) J a , b ( k ) is isomorphic to A₂(k) if and only if a = b.

Currently displaying 41 – 60 of 119