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A source of difficulty in profinite homotopy theory is that the profinite completion functor does not preserve finite products. In this note, we provide a new, checkable criterion on prospaces $X$ and $Y$ that guarantees that the profinite…

Algebraic Topology · Mathematics 2026-01-21 Peter J. Haine

For any type of fundamental groupoid scheme, we construct an algebraic cohomology theory for varieties with coefficients in the base field. This is a minor variant of \'etale cohomology, involving neither de Rham complexes nor…

Algebraic Geometry · Mathematics 2026-02-16 Hyuk Jun Kweon

We define the projective stable category of a coherent scheme. It is the homotopy category of an abelian model structure on the category of unbounded chain complexes of quasi-coherent sheaves. We study the cofibrant objects of this model…

Algebraic Topology · Mathematics 2019-03-27 Sergio Estrada , James Gillespie

In this article we extend Deligne's construction of Grothendieck's six operations on the derived category of torsion sheaves over the \'etale site of a scheme for morphisms of finite type to a larger class of morphisms. This class includes…

Algebraic Geometry · Mathematics 2019-02-14 Paul Hamacher

The goal of this paper is to prove an equivalence between the model categorical approach to pro-categories, as studied by Isaksen, Schlank and the first author, and the $\infty$-categorical approach, as developed by Lurie. Three…

Algebraic Topology · Mathematics 2017-02-01 Ilan Barnea , Yonatan Harpaz , Geoffroy Horel

Let $(X,\bar x)$ be a pointed connected noetherian scheme. In this note, we give characterizations for the vanishing of the second \'etale homotopy group $\pi^{\rm \'et}_2(X,\bar x)$ in terms of splitting profinite-\'etale covers of $X$,…

Algebraic Geometry · Mathematics 2026-02-27 Mohammed Moutand

Finite \'etale covers of a connected scheme $X$ are parametrised by the \'etale fundamental group via the monodromy correspondence. This was generalised to an exodromy correspondence for constructible sheaves, first in the topological…

Algebraic Geometry · Mathematics 2024-10-10 Remy van Dobben de Bruyn

We present some constructions of limits and colimits in pro-categories. These are critical tools in several applications. In particular, certain technical arguments concerning strict pro-maps are essential for a theorem about \'etale…

Category Theory · Mathematics 2007-05-23 Daniel C. Isaksen

Many important theorems in differential topology relate properties of manifolds to properties of their underlying homotopy types -- defined e.g. using the total singular complex or the \v{C}ech nerve of a good open cover. Upon embedding the…

Algebraic Topology · Mathematics 2023-09-06 Adrian Clough

We combine Homotopy Type Theory with axiomatic cohesion, expressing the latter internally with a version of "adjoint logic" in which the discretization and codiscretization modalities are characterized using a judgmental formalism of "crisp…

Category Theory · Mathematics 2017-04-26 Michael Shulman

The notion of a natural model of type theory is defined in terms of that of a representable natural transfomation of presheaves. It is shown that such models agree exactly with the concept of a category with families in the sense of Dybjer,…

Category Theory · Mathematics 2017-01-10 Steve Awodey

We review the shape theory of $\infty$-topoi, and relate it with the usual cohomology of locally constant sheaves. Additionally, a new localization of profinite spaces is defined which allows us to extend the \'etale realization functor of…

Algebraic Topology · Mathematics 2017-08-15 Joe Berner

We prove in this paper that for a quasi-compact and semi-separated (non necessarily noetherian) scheme X, the derived category of quasi-coherent sheaves over X, D(A_qc(X)), is a stable homotopy category in the sense of Hovey, Palmieri and…

Algebraic Geometry · Mathematics 2017-04-27 Leovigildo Alonso , Ana Jeremias , Marta Perez , Maria J. Vale

We study simplicial profinite groups with a view towards applications in profinite combinatorial group theory. This approach provides a natural framework to the concept of pro-$\mathfrak{C}$-presentation of a pro-$\mathfrak{C}$-group $G$ as…

Group Theory · Mathematics 2015-12-22 Andrey Mikhovich

This paper defines homology in homotopy type theory, in the process stable homotopy groups are also defined. Previous research in synthetic homotopy theory is relied on, in particular the definition of cohomology. This work lays the…

Logic · Mathematics 2018-12-27 Robert Graham

A lot of good properties of etale cohomology only hold for torsion coefficients. We use "enlargement of categories" as developed in http://arxiv.org/abs/math.CT/0408177 to define a cohomology theory that inherits the important properties of…

Algebraic Geometry · Mathematics 2007-05-23 Lars Brünjes , Christian Serpé

Homotopy type theory is an interpretation of Martin-L\"of's constructive type theory into abstract homotopy theory. There results a link between constructive mathematics and algebraic topology, providing topological semantics for…

Logic · Mathematics 2023-03-31 Steve Awodey , Nicola Gambino , Kristina Sojakova

We show that the weakly \'etale morphisms, used to define the pro-\'etale site of a scheme, are characterized by a lifting property similar to the one which characterizes formally \'etale morphisms. In order to prove this, we prove a…

Algebraic Geometry · Mathematics 2022-02-15 Aise Johan de Jong , Noah Olander

We prove that the category of profinite cosheaves valued in a pro-regular category (satisfying mild assumptions) is itself a pro-regular category. As a corollary, we extend Wilkes's cosheaf-bundle equivalence from profinite modules to…

Category Theory · Mathematics 2026-02-11 Jiacheng Tang

In this paper, we describe an algorithm that, for a smooth connected curve $X$ over a field $k$ with normal completion having arithmetic genus $p_a(X)$, a finite locally constant sheaf $\mathcal A$ on $X_{et}$ of abelian groups of torsion…

Algebraic Geometry · Mathematics 2017-11-20 Jinbi Jin