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In this work, we investigate an effective method for showing that functors between categories are left adjoints. The method applies to a large class of categories, namely locally finitely presentable categories, which are ubiquitous in…

Category Theory · Mathematics 2025-01-28 Simon Forest

We prove that the direct sums of extensions of scalars of relation modules are geometrically realisable as the second homotopy group of a finite 2-complex. We use this to exhibit a finite 2-complex with fundamental group the $(10,15)$ torus…

Algebraic Topology · Mathematics 2023-12-06 William Thomas

This paper reformulates Goodwillie calculus of $\infty$-categories including non-presentable $\infty$-categories. In the case of presentable $\infty$-categories our definition is equivalent to Heuts's~\cite{Heuts2018} work. As an…

Category Theory · Mathematics 2025-09-15 Yuki Kato

Generalizing a definition of homotopy fiber products of model categories, we give a definition of the homotopy limit of a diagram of left Quillen functors between model categories. As has been previously shown for homotopy fiber products,…

Algebraic Topology · Mathematics 2014-02-26 Julia E. Bergner

We examine various triangulated quotients of the module category of a finite group. We demonstrate that these are not compactly generated by the simple modules and present a modification of Rickard's Idempotent Module construction that…

Representation Theory · Mathematics 2007-05-23 Matthew Grime

Using the language of double categories we generalise a classical result on finite-product-preserving left Kan extensions, by Ad\'amek and Rosick\'y, to one on left Kan extensions that preserve algebraic structures defined by `suitable'…

Category Theory · Mathematics 2014-12-12 Seerp Roald Koudenburg

In a previous paper we introduced the concept of semiseparable functor. Here we continue our study of these functors in connection with idempotent (Cauchy) completion. To this aim, we introduce and investigate the notions of (co)reflection…

Category Theory · Mathematics 2023-06-13 Alessandro Ardizzoni , Lucrezia Bottegoni

We compare the colimit and 2-colimit of strict 2-functors in the 2-category of groupoids, over a certain type of posets. These posets are of special importance, as they correspond to coverings of a topological space. The main result of this…

Category Theory · Mathematics 2023-05-10 Ilia Pirashvili

We give a construction of triangulated categories as quotients of exact categories where the subclass of objects sent to zero is defined by a triple of functors. This includes the cases of homotopy and stable module categories. These…

Category Theory · Mathematics 2007-08-20 Matthew Grime

We show that indecomposable exact module categories over the category Rep H of representations of a finite-dimensional Hopf algebra H are classified by left comodule algebras, H-simple from the right and with trivial coinvariants, up to…

Quantum Algebra · Mathematics 2010-06-29 Nicolas Andruskiewitsch , Juan Martin Mombelli

Among cocomplete categories, the locally presentable ones can be defined as those with a strong generator consisting of presentable objects. Assuming Vop{\v{e}}nka's Principle, we prove that a cocomplete category is locally presentable iff…

Category Theory · Mathematics 2020-12-04 J. Adámek , A. Brooke-Taylor , T. Campion , L. Positselski , J. Rosický

We develop a 2-dimensional version of accessibility and presentability compatible with the formalism of flat pseudofunctors. First we give prerequisites on the different notions of 2-dimensional colimits, filteredness and cofinality; in…

Category Theory · Mathematics 2025-08-05 Ivan Di Liberti , Axel Osmond

A group completion functor Q is constructed in the category of algebras in simplicial sets over a cofibrant E_n-operad M. It is shown that Q defines a Bousfield-Friedander simplicial model category on M-algebras.

Algebraic Topology · Mathematics 2011-11-28 Manfred Stelzer

In this paper, we address the construction of homotopy bicategories of $(\infty,2)$-categories, which we take as being modeled by 2-fold Segal spaces. Our main result is the concrete construction of a functor $h_2$ from the category of…

Category Theory · Mathematics 2025-02-14 Jack Romö

In this short note, we provide a calculation of the Euler characteristic of a finite homotopy colimit of finite cell complexes, which depends only on the Euler characteristics of each space and resembles Mobius inversion. Versions of the…

Algebraic Topology · Mathematics 2018-11-07 John D. Berman

In this work, we study the notion of cofinal functor of $\infty$-bicategories with respect to the theory of partially lax colimits. The main result of this paper is a characterization of cofinal functors of $\infty$-bicategories via…

Algebraic Topology · Mathematics 2023-04-17 Fernando Abellán , Walker H. Stern

In this paper, we prove that the bounded derived category $D^b_{coh}(Y)$ of coherent sheaves on a separated scheme $Y$ of finite type over a field $\mathrm{k}$ of characteristic zero is homotopically finitely presented. This confirms a…

Algebraic Geometry · Mathematics 2025-02-10 Alexander I. Efimov

We introduce the compactness locus of a geometric functor between rigidly-compactly generated tensor-triangulated categories, and describe it for several examples arising in equivariant homotopy theory and algebraic geometry. It is a subset…

Category Theory · Mathematics 2019-01-29 Beren Sanders

We show that basic homotopical notions such as homotopy sets and groups, connected and truncated maps, cellular constructions and skeleta, etc., extend to the setting of $(\infty,\infty)$-categories, as well as to presentable categories…

Algebraic Topology · Mathematics 2026-04-16 David Gepner , Hadrian Heine

We proved in a previous work that Cattani-Sassone's higher dimensional transition systems can be interpreted as a small-orthogonality class of a topological locally finitely presentable category of weak higher dimensional transition…

Category Theory · Mathematics 2014-01-31 Philippe Gaucher