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In this monograph we develop various aspects of the homotopy theory of exact categories. We introduce different notions of compactness and generation in exact categories $E$, and use these to study model structures on categories of chain…

Category Theory · Mathematics 2021-07-27 Jack Kelly

We study Gorenstein categories. We show that such a category has Tate cohomological functors and Avramov-Martsinkovsky exact sequences connecting the Gorenstein relative, the absolute and the Tate cohomological functors. We show that such a…

Category Theory · Mathematics 2007-11-09 Edgar Enochs , Sergio Estrada , J. R. Garcia-Rozas

We construct examples of bounded below, noncontractible, acyclic complexes of finitely generated projective modules over some rings $S$, as well as bounded above, noncontractible, acyclic complexes of injective modules. The rings $S$ are…

Rings and Algebras · Mathematics 2024-05-06 Leonid Positselski

We define a new model structure on the category of small categories, which is intimately related to the notion of coverings and fundamental groups of small categories. Fibrant objects in the model structure coincide with groupoids, and the…

Category Theory · Mathematics 2012-05-08 Kohei Tanaka

We extend the framework of combinatorial model categories, so that the category of small presheaves over large indexing categories and ind-categories would be embraced by the new machinery called class-combinatorial model categories. The…

Algebraic Topology · Mathematics 2019-12-06 Boris Chorny , Jiří Rosický

We show that projective structures with torsion are described in terms of affine connections in a parallel way as in the torsion-free case which is done by Kobayashi and Nagano. For this, we make use of a bundle of formal frames, which is a…

Differential Geometry · Mathematics 2026-02-12 Taro Asuke

We describe the integral equivariant cohomology ring of a weighted projective space in terms of piecewise polynomials, and thence by generators and relations. We deduce that the ring is a perfect invariant, and prove a Chern class formula…

Algebraic Topology · Mathematics 2009-04-15 Anthony Bahri , Matthias Franz , Nigel Ray

The theory of $N$-complexes is a generalization of both ordinary chain complexes and graded objects. Hence it yields deeper insight in the structure of these and offers a broader range of applications. This work generalizes the tensor…

Category Theory · Mathematics 2024-02-01 Felix Küng

We present a class of Poisson structures on trivial extension algebras which generalize some known structures induced by Poisson modules. We show that there exists a one-to-one correspondence between such a class of Poisson structures and…

Rings and Algebras · Mathematics 2023-08-30 D. García-Beltrán , J. C. Ruíz-Pantaleón , Yu. Vorobiev

A countable structure is said to be extendible if it has the same Scott sentence as some uncountable structure. Rigid structures are not extendible. We give an example of an extendible model with a rigid elementary extension.

Logic · Mathematics 2017-11-29 Paul B. Larson , Saharon Shelah

We obtain several results concerning the concept of isotypic structures. Namely we prove that any field of finite transcendence degree over a prime subfield is defined by types; then we construct isotypic but not isomorphic structures with…

Logic · Mathematics 2025-06-18 Pavel Gvozdevsky

We introduce a notion of a connection on a coherent sheaf on a weighted projective line (in the sense of Geigle and Lenzing). Using a theorem of Huebner and Lenzing we show, under a mild hypothesis, that if one considers coherent sheaves…

Algebraic Geometry · Mathematics 2009-04-23 William Crawley-Boevey

We present a uniform theory of constructible sheaves on arbitrary schemes with coefficients in topological or even condensed rings. This is accomplished by defining lisse sheaves to be the dualizable objects in the derived infinity-category…

Algebraic Geometry · Mathematics 2023-05-30 Tamir Hemo , Timo Richarz , Jakob Scholbach

The homotopy category of complexes of projective left-modules over any reasonably nice ring is proved to be a compactly generated triangulated category, and a duality is given between its subcategory of compact objects and the finite…

Rings and Algebras · Mathematics 2007-05-23 Peter Jorgensen

In the paper "Cotorsion Pairs in C(R-Mod)", the authors construct an abelian model structure on the category of chain complexes Ch(R), where the class of cofibrant objects is given by the class of degreewise projective chain complexes.…

Category Theory · Mathematics 2012-07-03 Marco Pérez

We prove the (2,1)-categorical analogue of the small object argument and give a (2,1)-model structure on the category of small coherent categories, coherent functors and natural isomorphisms. It is induced by a higher dimensional example of…

Category Theory · Mathematics 2022-02-17 Kristóf Kanalas

I classify projective modules over idempotent semirings that are free on a monoid. The analysis extends to the case of the semiring of convex, piecewise-affine functions on a polyhedron, for which projective modules correspond to convex…

Commutative Algebra · Mathematics 2015-07-28 Andrew W. Macpherson

We prove the existence of a model structure on the category of stratified simplicial sets whose fibrant objects are precisely $n$-complicial sets, which are a proposed model for $(\infty,n)$-categories, based on previous work of Verity and…

Algebraic Topology · Mathematics 2020-06-03 Viktoriya Ozornova , Martina Rovelli

We show that C if is a proper model category, then the pro-category pro-C has a strict model structure in which the weak equivalences are the levelwise weak equivalences. The strict model structure is the starting point for many homotopy…

Algebraic Topology · Mathematics 2007-05-23 Daniel C. Isaksen

We build a model structure from the simple point of departure of a structured interval in a monoidal category - more generally, a structured cylinder and a structured co-cylinder in a category.

Category Theory · Mathematics 2016-04-26 Richard Williamson