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We prove that any digraph Brown functor -- i.e. a contravariant functor from the homotopy category of finite directed graphs to the category of abelian groups, satisfying the triviality axiom, the additivity axiom, and the Mayer-Vietoris…

Algebraic Topology · Mathematics 2025-08-04 Hsuan-Yi Liao , Zachary McGuirk , Dang Khoa Nguyen , Byungdo Park

We define quasi--locally presentable categories as big unions of coreflective subcategories which are locally presentable. Under appropriate hypotheses we prove a representability theorem for exact contravariant functors defined on a…

Category Theory · Mathematics 2012-05-11 George Ciprian Modoi

We prove general adjoint functor theorems for weakly (co)complete $n$-categories. This class of $n$-categories includes the homotopy $n$-categories of (co)complete $\infty$-categories, so these $n$-categories do not admit all small…

Category Theory · Mathematics 2022-08-03 Hoang Kim Nguyen , George Raptis , Christoph Schrade

We call product generator of an additive category a fixed object satisfying the property that every other object is a direct factor of a product of copies of it. In this paper we start with an additive category with products and images,…

Category Theory · Mathematics 2013-05-28 George Ciprian Modoi

In this paper we prove two theorems which resemble the classical cohomological and homological Brown representability theorems. The main difference is that our results classify small contravariant functors from spaces to spaces up to weak…

Algebraic Topology · Mathematics 2013-12-05 Boris Chorny

Adjoint functor theorems give necessary and sufficient conditions for a functor to admit an adjoint. In this paper we prove general adjoint functor theorems for functors between $\infty$-categories. One of our main results is an…

Category Theory · Mathematics 2019-09-18 Hoang Kim Nguyen , George Raptis , Christoph Schrade

In this paper, we deal with two types of representability. The first is a variant of the Brown representability theorem in the spirit of Rouquier and Neeman. The second is a variant of the Brown-Adams representability. If $A$ is a…

Category Theory · Mathematics 2025-04-22 George Ciprian Modoi

We establish a relative version of the abstract "affine representability" theorem in ${\mathbb A}^1$--homotopy theory from Part I of this paper. We then prove some ${\mathbb A}^1$--invariance statements for generically trivial torsors under…

Algebraic Geometry · Mathematics 2018-03-16 Aravind Asok , Marc Hoyois , Matthias Wendt

We prove the following result of V. Voevodsky. If $S$ is a finite dimensional noetherian scheme such that $S=\cup_\alpha\Spec(R_\alpha)$ for {\em countable} rings $R_\alpha$, then the stable motivic homotopy category over $S$ satisfies…

Algebraic Geometry · Mathematics 2009-09-11 N. Naumann , M. Spitzweck

Let T be a triangulated category with coproducts, C the full subcategory of compact objects in T. If T is the homotopy category of spectra, Adams proved the following in [Adams71]: All contravariant homological functors C --> Ab are the…

Algebraic Topology · Mathematics 2017-07-11 J. Daniel Christensen , Bernhard Keller , Amnon Neeman

We prove two representability theorems, up to homotopy, for presheaves taking values in a closed symmetric combinatorial model category \cat V. The first theorem resembles the Freyd representability theorem, the second theorem is closer to…

Algebraic Topology · Mathematics 2019-07-25 David Blanc , Boris Chorny

Motivated by the study of the interrelation between functorial and algebraic quantum field theory, we point out that on any locally trivial bundle of compact groups, representations up to homotopy are enough to separate points by means of…

Differential Geometry · Mathematics 2015-12-03 Giorgio Trentinaglia , Chenchang Zhu

Our main observation is that the contravariant functor Spec on the category of commutative monoids is representable. We discuss a few consequences of this fact. In particular, we give an efficient way of calculating the Spec(M) of a…

Algebraic Geometry · Mathematics 2012-07-17 Ilia Pirashvili

For a triangulated category with products we develop a method for constructing a nice set of cogenerators, allowing us to prove a formal criterion in order to satisfy Brown representability for covariant functors. We apply this criterion…

Category Theory · Mathematics 2014-10-21 George Ciprian Modoi

We prove new Brown representability theorems for triangulated categories using metric techniques as introduced in the work of Neeman. In the setting of algebraic geometry, this gives us new representability theorems for homological and…

Algebraic Geometry · Mathematics 2025-04-17 Kabeer Manali Rahul

This is the second paper in a series. In part I we developed deformation theory of objects in homotopy and derived categories of DG categories. Here we extend these (derived) deformation functors to an appropriate bicategory of artinian DG…

Algebraic Geometry · Mathematics 2018-08-13 Alexander I. Efimov , Valery A. Lunts , Dmitri O. Orlov

Consider a complete abelian category which has an injective cogenerator. If its derived category is left--complete we show that the dual of this derived category satisfies Brown representability. In particular this is true for the derived…

Category Theory · Mathematics 2016-06-28 George Ciprian Modoi

For odd and for even involutive, commutative residuated chains a representation theorem is presented in this paper by means of direct systems of abelian o-groups equipped with further structure. This generalizes the corresponding result of…

Rings and Algebras · Mathematics 2023-06-27 Sándor Jenei

We relate endotrivial representations of a finite group in characteristic p to equivariant line bundles on the simplicial complex of non-trivial p-subgroups, by means of weak homomorphisms.

Group Theory · Mathematics 2018-12-19 Paul Balmer

We show that every nontrivial finite or infinite connected directed graph with loops and at least one vertex without a loop is uniquely representable as a Cartesian or weak Cartesian product of prime graphs. For finite graphs the…

Combinatorics · Mathematics 2017-02-21 Wilfried Imrich , Iztok Peterin
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