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In this short note we show that under very mild conditions on a functor between exact categories $F:\mathcal{D}\rightarrow\mathcal{E}$ it is possible to derive $F$ at the level of unbounded complexes. We also give applications to deriving…

Category Theory · Mathematics 2021-04-02 Jack Kelly

Let $G$ be a split reductive group over a local field $\bK$, and let $G((t))$ be the corresponding loop group. In \cite{GK} we have introduced the notion of a representation of (the group of $\bK$-points) of $G((t))$ on a pro-vector space.…

Representation Theory · Mathematics 2007-05-23 Dennis Gaitsgory , David Kazhdan

Graduated locally finitely presentable categories are introduced, examples include categories of sets, vector spaces, posets, presheaves and Boolean algebras. A finitary functor between graduated locally finitely presentable categories is…

Category Theory · Mathematics 2024-02-06 Jirí Adámek , Lurdes Sousa

For G a profinite group, we construct an equivalence between rational G-Mackey functors and a certain full subcategory of G-sheaves over the space of closed subgroups of G called Weyl-G-sheaves. This subcategory consists of those sheaves…

Algebraic Topology · Mathematics 2022-04-29 David Barnes , Danny Sugrue

We classify the primitive idempotents of the $p$-local complex representation ring of a finite group $G$ in terms of the cyclic subgroups of order prime to $p$ and show that they all come from idempotents of the Burnside ring. Our results…

Algebraic Topology · Mathematics 2020-10-12 Benjamin Böhme

An approach to identify the normal subgroups determined by ideals in free group rings with the help of the derived functors of non-additive functors is explored. A similar approach, i.e., via derived functors, for computing limits of…

Group Theory · Mathematics 2016-05-27 Roman Mikhailov , Inder Bir S. Passi

We gather tools for proving the inductive McKay--Navarro (or Galois--McKay) condition for groups of Lie type and odd primes. We use this to establish a bijection in the case of quasisimple groups of Lie type A satisfying the equivariance…

Representation Theory · Mathematics 2025-06-23 Lucas Ruhstorfer , A. A. Schaeffer Fry , Britta Späth , Jay Taylor

We study finitary 2-categories associated to dual projection functors for finite dimensional associative algebras. In the case of path algebras of admissible tree quivers (which includes all Dynkin quivers of type A) we show that the monoid…

Representation Theory · Mathematics 2017-05-10 Anna-Louise Grensing , Volodymyr Mazorchuk

In this note, we extend the inductions and restrictions of modules over finite groups to non-injective group homomorphisms, establishing transitivity, Frobenius reciprocity, Mackey's formula, etc.

Representation Theory · Mathematics 2024-10-31 Conghui Li , Yuting Tian

Suppose that $G$ is a finite group and $H$ is a nilpotent subgroup of $G$. If a character of $H$ induces an irreducible character of $G$, then the generalized Fitting subgroup of $G$ is nilpotent.

Representation Theory · Mathematics 2019-02-27 Zoltan Halasi , Attila Maroti , Gabriel Navarro , Pham Huu Tiep

We reformulate the inductive McKay condition, from Isaacs-Malle-Navarro, and apply the new criterion to simple groups of Lie type, when the prime is the defining characteristic p. Thereby we make use of a recent result of Maslowski. This…

Representation Theory · Mathematics 2014-02-26 Britta Späth

For a finite group $G$, a semi-Mackey (resp. Tambara) functor is regarded as a $G$-bivariant analog of a commutative monoid (resp. ring). As such, some naive algebraic constructions are generalized to this $G$-bivariant setting. In this…

Category Theory · Mathematics 2011-03-22 Hiroyuki Nakaoka

A correspondence functor is a functor from the category of finite sets and correspondences to the category of $k$-modules, where $k$ is a commutative ring. We determine exactly which simple correspondence functors are projective. Moreover,…

Representation Theory · Mathematics 2019-02-27 Serge Bouc , Jacques Thévenaz

We will give quiver presentations of the Grothendieck constructions of functors from a small category to the 2-category of $\Bbbk$-categories for a commutative ring $\Bbbk$.

Rings and Algebras · Mathematics 2011-11-18 Hideto Asashiba , Mayumi Kimura

We construct Nakayama functors on proper abelian subcategories of triangulated categories with a Serre functor using approximation theory. This, in turn, allows for the construction of Auslander-Reiten translates. As a result, we prove that…

Representation Theory · Mathematics 2025-08-06 David Nkansah

We show that the Green biset functor $R_{\mathbb{C}}$ of complex characters over $\mathbb{Z}$, is not separable, i.e. it is not projective as a bimodule over itself. Also, we show that $RB_G$, the Burnside biset functor shifted by a finite…

Group Theory · Mathematics 2026-04-10 Serge Bouc , Nadia Romero

We show that the unbounded derived category of a Grothendieck category with enough projective objects is the base category of a derivator whose category of diagrams is the full 2-category of small categories. With this structure, we give a…

Category Theory · Mathematics 2024-05-17 Leovigildo Alonso , Beatriz Álvarez , Ana Jeremías

For any algebra morphism in a monoidal category, we provide sufficient conditions (which are also necessary if the unit is a left tensor generator) for the attached induction functor being semiseparable. Under mild assumptions, we prove…

Category Theory · Mathematics 2026-02-04 Lucrezia Bottegoni , Zhenbang Zuo

We give an introduction to constructive category theory by answering two guiding computational questions. The first question is: how do we compute the set of all natural transformations between two finitely presented functors like…

Category Theory · Mathematics 2019-08-13 Sebastian Posur

In this paper we establish the Mackey formula for groupoids, extending the well known formula in abstract groups context. This formula involves the notion of groupoid-biset, its orbit set and the tensor product over groupoids, as well as…

Group Theory · Mathematics 2018-12-12 Laiachi El Kaoutit , Leonardo Spinosa