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Effective bounds for the finite number of surjective holomorphic maps between canonically polarized compact complex manifolds of any dimension with fixed domain are proven. Both the case of a fixed target and the case of varying targets are…

Algebraic Geometry · Mathematics 2007-05-23 Gordon Heier

We consider limits over categories of extensions and show how certain well-known functors on the category of groups turn out as such limits. We also discuss higher (or derived) limits over categories of extensions.

Category Theory · Mathematics 2009-05-21 Roman Mikhailov , Inder Bir S. Passi

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

For equivariant stable homotopy theory, equivariant KK-theory and equivariant derived categories, we show how restriction to a subgroup of finite index yields a finite commutative separable extension, analogous to finite \'etale extensions…

Category Theory · Mathematics 2015-11-16 Paul Balmer , Ivo Dell'Ambrogio , Beren Sanders

In this paper, we construct a comparison map from the topological fundamental group to the pro-\'etale fundamental group for a complex variety.

Algebraic Geometry · Mathematics 2023-08-17 Jiu-Kang Yu , Lei Zhang

We introduce notions of lax semiadditive and lax additive $(\infty,2)$-categories, categorifying the classical notions of semiadditive and additive 1-categories. To establish a well-behaved axiomatic framework, we develop a calculus of lax…

Category Theory · Mathematics 2025-11-18 Merlin Christ , Tobias Dyckerhoff , Tashi Walde

We introduce the notion of a definable category--a category equivalent to a full subcategory of a locally finitely presentable category that is closed under products, directed colimits and pure subobjects. Definable subcategories are…

Category Theory · Mathematics 2016-12-13 Amit Kuber , Jiří Rosický

We show that in a category with pullbacks, arbitrary sifted colimits may be constructed as filtered colimits of reflexive coequalizers. This implies that "lex sifted colimits", in the sense of Garner--Lack, decompose as Barr-exactness plus…

Category Theory · Mathematics 2021-12-10 Ruiyuan Chen

Coclass theory can be used to define infinite families of finite p-groups of a fixed coclass. It is conjectured that the groups in one of these infinite families all have isomorphic mod-p cohomology rings. Here we prove that almost all…

Group Theory · Mathematics 2015-03-31 Bettina Eick , David J. Green

The theory of derivators provides a convenient abstract setting for computing with homotopy limits and colimits. In enriched homotopy theory, the analogues of homotopy (co)limits are weighted homotopy (co)limits. In this thesis, we develop…

Algebraic Topology · Mathematics 2020-10-16 James Richardson

We introduce the notion of $\pi$-cosupport as a new tool for the stable module category of a finite group scheme. In the case of a finite group, we use this to give a new proof of the classification of tensor ideal localising subcategories.…

Representation Theory · Mathematics 2017-01-09 Dave Benson , Srikanth B. Iyengar , Henning Krause , Julia Pevtsova

Many kinds of categorical structure require the existence of finite limits, of colimits of some specified type, and of "exactness" conditions between the finite limits and the specified colimits. Some examples are the notions of regular, or…

Category Theory · Mathematics 2012-02-20 Richard Garner , Stephen Lack

Let $\mathcal A$ be a Hom-finite abelian category with enough projectives. In this note, we show that any covariantly finite $\tau$-rigid subcategory is contained in a support $\tau$-tilting subcategory. We also show that support…

Representation Theory · Mathematics 2023-02-07 Yu Liu , Panyue Zhou

We apply the theory of weighted bicategorical colimits to study the problem of existence and computation of such colimits of birepresentations of finitary bicategories. The main application of our results is the complete classification of…

Representation Theory · Mathematics 2024-08-28 Mateusz Stroiński

We prove and explain several classical formulae for homotopy (co)limits in general (combinatorial) model categories which are not necessarily simplicially enriched. Importantly, we prove versions of the Bousfield-Kan formula and the fat…

Category Theory · Mathematics 2019-09-04 Sergey Arkhipov , Sebastian Ørsted

The Hom closed colocalizing subcategories of the stable module category of a finite group are classified. Along the way, the colocalizing subcategories of the homotopy category of injectives over an exterior algebra, and the derived…

Representation Theory · Mathematics 2011-02-15 Dave Benson , Srikanth B. Iyengar , Henning Krause

We study 2-monads and their algebras using a Cat-enriched version of Quillen model categories, emphasizing the parallels between the homotopical and 2-categorical points of view. Every 2-category with finite limits and colimits has a…

Category Theory · Mathematics 2010-09-10 Stephen Lack

The main objective of this paper is to construct a homotopy colimit functor on a category of functors taking values in the model category of quasi-categories.

Category Theory · Mathematics 2020-07-21 Amit Sharma

In this paper we consider a family of nested t-structures given by silting objects and construct a silting object corresponding to the intersection of aisles of these t-structures as a homotopy colimit. The dual construction for the…

Representation Theory · Mathematics 2026-05-11 Rosanna Laking , Alexandra Zvonareva

Let $I$,$J$ be small categories and $C:I\times J@>>>\CAT$ a functor to the category of small categories. We show that if $I$ has a final object then the canonical map…

Algebraic Topology · Mathematics 2011-08-29 Guillermo Cortiñas