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We consider three (2-)categories and their (anti-)equivalence. They are the category of small abelian categories and exact functors, the category of definable additive categories and interpretation functors, the category of locally coherent…

Category Theory · Mathematics 2012-02-03 Mike Prest

We investigate categoricity of abstract elementary classes without any remnants of compactness (like non-definability of well ordering, existence of E.M. models or existence of large cardinals). We prove (assuming a weak version of GCH…

Logic · Mathematics 2016-09-07 Saharon Shelah

Accessible categories admit a purely category-theoretic replacement for cardinality: the internal size. Generalizing results and methods from arXiv:1708.06782, we examine set-theoretic problems related to internal sizes and prove several…

Logic · Mathematics 2019-06-06 Michael Lieberman , Jiří Rosický , Sebastien Vasey

For any commutative ring $R$, we show that the categories of $R$-coalgebras and cocommutative $R$-coalgebras are locally $\aleph_1$-presentable, while the categories of $R$-flat $R$-coalgebras are $\aleph_1$-accessible. Similarly, for any…

Rings and Algebras · Mathematics 2025-07-25 Leonid Positselski

We show that the category of abstract elementary classes (AECs) and concrete functors is closed under constructions of "limit type," which generalizes the approach of Mariano, Zambrano and Villaveces away from the syntactically oriented…

Logic · Mathematics 2020-12-07 M. Lieberman , J. Rosický

We give a short overview of the proof of Shelah's eventual categoricity conjecture in universal classes with amalgamation in arXiv:1506.07024 .

Logic · Mathematics 2015-12-01 Sebastien Vasey

We introduce subclasses of exact categories in terms of admissible intersections or admissible sums or both at the same time. These categories are recently studied by Br\"ustle, Hassoun, Shah, Tattar and Wegner to give characterisations of…

Representation Theory · Mathematics 2020-06-08 Souheila Hassoun , Sunny Roy

Let K be an abstract elementary class with amalgamation, and Lowenheim Skolem number LS(K). We prove that for a suitable Hanf number chi_0 if chi_0 < lambda_0 <= lambda_1, and K is categorical in lambda^+_1 then it is categorical in…

Logic · Mathematics 2016-09-07 Saharon Shelah

Classification theory of elementary classes deals with first order (elementary) classes of structures (i.e. fixing a set T of first order sentences, we investigate the class of models of T with the elementary submodel notion). It tries to…

Logic · Mathematics 2009-03-23 Saharon Shelah

In this expository paper we explain in detail how to construct bicategorical colimits of several kinds of tensor categories, for example essentially small finitely cocomplete K-linear tensor categories. The constructions are direct and…

Category Theory · Mathematics 2020-01-29 Martin Brandenburg

We study abstract elementary classes (AECs) that, in $\aleph_0$, have amalgamation, joint embedding, no maximal models and are stable (in terms of the number of orbital types). Assuming a locality property for types, we prove that such…

Logic · Mathematics 2018-05-31 Saharon Shelah , Sebastien Vasey

We give a purely category-theoretic proof of the result of Makkai and Par\'e saying that the category $\bf Lin$ of linearly ordered sets and order preserving injective mappings is a minimal finitely accessible category. We also discuss the…

Category Theory · Mathematics 2022-02-08 Jiří Rosický

We show that complete Segal spaces and Segal categories are Quillen equivalent to quasi-categories.

Algebraic Topology · Mathematics 2007-05-23 Andre Joyal , Myles Tierney

This paper is part of a program initiated by Saharon Shelah to extend the model theory of first order logic to the non-elementary setting of abstract elementary classes (AECs). An abstract elementary class is a semantic generalization of…

Logic · Mathematics 2017-04-13 Monica M. VanDieren , Sebastien Vasey

In this note we discuss Morita equivalence classes of arbitrary finitely presented algebras

Rings and Algebras · Mathematics 2018-06-05 Adel Alahmadi , Hamed Alsulami , Efim Zelmanov

We study the $2$-categories BIon, of (generalized) bounded ionads, and $\text{Acc}_\omega$, of accessible categories with directed colimits, as an abstract framework to approach formal model theory. We relate them to topoi and (lex)…

Category Theory · Mathematics 2025-08-05 Ivan Di Liberti

For each deconstructible class of modules $\mathcal D$, we prove that the categoricity of $\mathcal D$ in a big cardinal is equivalent to its categoricity in a tail of cardinals. We also prove Shelah's Categoricity Conjecture for $(\mathcal…

Logic · Mathematics 2023-10-09 Jan Trlifaj

In this article, the theory of sheaves is studied from a categorical point of view. This perspective vastly generalizes the usual theory of sheaves of sets to a more abstract setting which allows us to investigate the theory of sheaves with…

Commutative Algebra · Mathematics 2017-09-22 Abolfazl Tarizadeh

We discuss relations between the motives of two varieties with equivalent derived categories of coherent sheaves.

Algebraic Geometry · Mathematics 2015-06-26 Dmitri Orlov

This article introduces Hilbert $*$-categories: an abstraction of categories with similar algebraic and analytic properties to the categories of real, complex, and quaternionic Hilbert spaces and bounded linear maps. Other examples include…

Category Theory · Mathematics 2025-12-09 Matthew Di Meglio , Chris Heunen