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An example of a cocomplete abelian category that is not complete is constructed.

Category Theory · Mathematics 2018-05-29 Jeremy Rickard

Internal categories feature notions of limit and completeness, as originally proposed in the context of the effective topos. This paper sets out the theory of internal completeness in a general context, spelling out the details of the…

Category Theory · Mathematics 2020-04-21 Enrico Ghiorzi

We prove that the 2-category of skeletally small abelian categories with exact monoidal structures is anti-equivalent to the 2-category of fp-hom-closed definable additive categories satisfying an exactness criterion. For a fixed finitely…

Representation Theory · Mathematics 2020-10-26 Rose Wagstaffe

We show that Quillen's small object argument works for exact categories under very mild conditions. This has immediate applications to cotorsion pairs and their relation to the existence of certain triangulated adjoint functors and model…

Category Theory · Mathematics 2011-07-28 Manuel Saorin , Jan Stovicek

We explain why the naive definition of a natural exact category structure on complete, separated topological vector spaces with linear topology fails. In particular, contrary to arXiv:0711.2527, the category of such topological vector…

Category Theory · Mathematics 2024-05-16 Leonid Positselski

Proto-exact and parabelian categories serve as non-additive analogues of exact and quasi-abelian categories, respectively. They give rise to algebraic K-theory and Hall algebras similarly to the additive setting. We show that every…

Representation Theory · Mathematics 2025-03-11 Sergey Mozgovoy

We prove a general theorem which includes most notions of "exact completion". The theorem is that "k-ary exact categories" are a reflective sub-2-category of "k-ary sites", for any regular cardinal k. A k-ary exact category is an exact…

Category Theory · Mathematics 2012-09-06 Michael Shulman

In this paper we introduce $n\mathbb{Z}$-abelian and $n\mathbb{Z}$-exact categories by axiomatising properties of $n\mathbb{Z}$-cluster tilting subcategories. We study this categories and show that every $n\mathbb{Z}$-cluster tilting…

Category Theory · Mathematics 2022-02-15 Ramin Ebrahimi , Alireza Nasr-Isfahani

We show that for a given exact category, there exists a bijection between semibricks (pairwise Hom-orthogonal set of bricks) and length wide subcategories (exact extension-closed length abelian subcategories). In particular, we show that a…

Category Theory · Mathematics 2022-08-08 Haruhisa Enomoto

This paper is concerned with the taxonomy of finitely complete categories, based on 'matrix properties' - these are a particular type of exactness properties that can be represented by integer matrices. In particular, the main result of the…

Category Theory · Mathematics 2022-05-14 Michael Hoefnagel , Pierre-Alain Jacqmin , Zurab Janelidze

We call a finitely complete category algebraically coherent when the change-of-base functors of its fibration of points are coherent, which means that they preserve finite limits and jointly strongly epimorphic pairs of arrows. We give…

Category Theory · Mathematics 2015-12-10 Alan S. Cigoli , James R. A. Gray , Tim Van der Linden

This paper is the first part of a series that investigates the existence of $n$-exact structures on idempotent complete additive categories for positive integers $n$. It is shown that every idempotent complete additive category has a unique…

Category Theory · Mathematics 2024-10-08 Carlo Klapproth

Let $\mathscr{F}$ be an $(n+2)$-angulated Krull-Schmidt category and $\mathscr{A} \subset \mathscr{F}$ an $n$-extension closed, additive and full subcategory with $\operatorname{Hom}_{\mathscr{F}}(\Sigma_n \mathscr{A}, \mathscr{A}) = 0$.…

Representation Theory · Mathematics 2021-08-23 Carlo Klapproth

We relate the theory of purity of a locally finitely presented category with products to the study of exact structures on the full subcategory of finitely presented objects. Properties in the context of purity are translated to properties…

Representation Theory · Mathematics 2026-02-16 Kevin Schlegel

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 define fully exact module categories, a subclass of exact module categories over a finite braided tensor category that is stable under the relative Deligne product. In contrast, we demonstrate with examples in both zero and non-zero…

Quantum Algebra · Mathematics 2026-01-30 Azat M. Gainutdinov , Robert Laugwitz

Sieg and Wegner showed that the stable exact sequences define a maximal exact structure (in the sense of Quillen) in any pre-abelian category. We generalize this result for weakly idempotent complete additive categories.

Category Theory · Mathematics 2011-06-09 Septimiu Crivei

Let A and B be abelian categories with enough projective and injective objects, and T : A-B a left exact additive functor. Then one has a comma category (B*T). It is shown that If T : A-B is X-exact, then (*X, X) is a (hereditary) cotorsion…

Category Theory · Mathematics 2023-10-25 Yuan Yuan , Jian He , Dejun Wu

Extensivity of a category may be described as a property of coproducts in the category, namely, that they are disjoint and universal. An alternative viewpoint is that it is a property of morphisms in a category. This paper explores this…

Category Theory · Mathematics 2025-02-19 Michael Hoefnagel , Emma Theart

We define admissible and weakly admissible subcategories in exact categories and prove that the former induce semi-orthogonal decompositions on the derived categories. We develop the theory of thin exact categories, an exact-category…

Representation Theory · Mathematics 2024-06-25 Agnieszka Bodzenta , Alexey Bondal