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We consider the contraderived category of left contramodules over a right linear topological ring $\mathfrak R$ with a countable base of neighborhoods of zero. Equivalently, this is the homotopy category of unbounded complexes of projective…

Category Theory · Mathematics 2024-12-31 Leonid Positselski , Jan Stovicek

We achieve an extremely useful description (up to isomorphism) of the Leavitt path algebra $L_K(E)$ of a finite graph $E$ with coefficients in a field $K$ as a direct sum of matrix rings over $K$, direct sum with a corner of the Leavitt…

Rings and Algebras · Mathematics 2019-02-12 Gene Abrams , T. G. Nam

The construction of the Leavitt path algebra associated to a directed graph $E$ is extended to incorporate a family $C$ consisting of partitions of the sets of edges emanating from the vertices of $E$. The new algebras, $L_K(E,C)$, are…

Rings and Algebras · Mathematics 2015-03-17 P. Ara , K. R. Goodearl

We prove an algebraic version of the Gauge-Invariant Uniqueness Theorem, a result which gives information about the injectivity of certain homomorphisms between ${\mathbb Z}$-graded algebras. As our main application of this theorem, we…

Rings and Algebras · Mathematics 2008-02-04 G. Abrams , P. N. Ánh , A. Louly , E. Pardo

Let $X$ be any rational surface. We construct a tilting bundle $T$ on $X$. Moreover, we can choose $T$ in such way that its endomorphism algebra is quasi-hereditary. In particular, the bounded derived category of coherent sheaves on $X$ is…

Algebraic Geometry · Mathematics 2017-06-27 Lutz Hille , Markus Perling

An important example of a model category is the category of unbounded chain complexes of R-modules, which has as its homotopy category the derived category of the ring R. This example shows that traditional homological algebra is…

Algebraic Topology · Mathematics 2007-05-23 J. Daniel Christensen

The aim of this note is threefold. The first is to obtain a simple characterization of relative constructible sheaves when the parameter space is projective. The second is to study the relative Fourier-Mukai for relative constructible…

Algebraic Geometry · Mathematics 2025-08-19 Luisa Fiorot , Teresa Monteiro Fernandes

The aim of this paper is to give new characterizations of some fundamental issues about idempotents. In the general setting of adjointable operators on Hilbert $C^*$-modules, a new term of quasi-projection pair is introduced. For each…

Operator Algebras · Mathematics 2025-08-15 Xiaoyi Tian , Qingxiang Xu , Chunhong Fu

We show that the endomorphism ring of any nonzero finitely generated projective module over the Leavitt path algebra $L_K(E)$ of an arbitrary graph $E$ with coefficients in a field $K$ is isomorphic to a Steinberg algebra. This yields in…

Rings and Algebras · Mathematics 2019-09-10 Gene Abrams , Mikhailo Dokuchaev , T. G. Nam

A method of constructing (finitely generated and projective) right module structure on a finitely generated projective left module over an algebra is presented. This leads to a construction of a first order differential calculus on such a…

Quantum Algebra · Mathematics 2011-07-21 Tomasz Brzeziński

For any row-finite graph $E$ and any field $K$ we construct the {\its Leavitt path algebra} $L(E)$ having coefficients in $K$. When $K$ is the field of complex numbers, then $L(E)$ is the algebraic analog of the Cuntz Krieger algebra…

Rings and Algebras · Mathematics 2007-05-23 G. Abrams , G. Aranda Pino

We introduce the notion of balanced pair of additive subcategories in an abelian category. We give sufficient conditions under which the balanced pair of subcategories gives rise to equivalent homotopy categories of complexes. As an…

Rings and Algebras · Mathematics 2010-11-23 Xiao-Wu Chen

In this paper we completely describe graphically Leavitt path algebras with bounded index of nilpotence. We show that the Leavitt path algebra $L_{K}(E)$ has index of nilpotence at most $n$ if and only if no cycle in the graph $E$ has an…

Rings and Algebras · Mathematics 2018-09-19 K. M. Rangaswamy , Ashish K. Srivastava

In this paper several characterizations of semi-compact modules are given. Among other results, we study rings whose semi-compact modules are injective. We introduce the property $\Sigma$-semi-compact for modules and we characterize the…

Commutative Algebra · Mathematics 2022-03-08 Mahmood Behboodi , François Couchot , Seyed Hossein Shojaee

A Leavitt labelled path algebra over a commutative unital ring is associated with a labelled space, generalizing Leavitt path algebras associated with graphs and ultragraphs as well as torsion-free commutative algebras generated by…

Rings and Algebras · Mathematics 2021-06-14 Giuliano Boava , Gilles G. de Castro , Daniel Gonçalves , Daniel W. van Wyk

We provide a complete answer to the question "When is a quotient of a Leavitt path algebra isomorphic to a Leavitt path algebra?" in terms of the interaction of the kernel of the quotient homomorphism with the cycles of the digraph. A key…

Rings and Algebras · Mathematics 2025-06-10 Ayten Koç , Murad Özaydın

We consider principal fibre bundles with a given connection and construct almost complex structures on the total space if the adjoint bundle is isomorphic to the tangent bundle of the base. We derive the integrability condition. If the…

Differential Geometry · Mathematics 2017-02-15 Raphael Zentner

We characterize projective objects in the category of internal crossed modules within any semi-abelian category. When this category forms a variety of algebras, the internal crossed modules again constitute a semi-abelian variety, ensuring…

Category Theory · Mathematics 2026-01-09 Maxime Culot

We show that for any singular dominant integral weight $\lambda$ of a complex semisimple Lie algebra $\mathfrak{g}$, the endomorphism algebra $B$ of any projective-injective module of the parabolic BGG category…

Representation Theory · Mathematics 2018-09-11 Jun Hu , Ngau Lam

Let G be a complex algebraic semi-simple adjoint group and X a smooth complete symmetric G-variety. Let L_i be the irreducible G-equivariant intersection cohomology complexes on X, and L the direct sum of the L_i. Let E= Ext(L,L) be the…

Algebraic Geometry · Mathematics 2007-05-23 Stéphane Guillermou
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