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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

Using methods from algebraic topology and group cohomology, I pursue Grothendieck's question on equality of geometric and cohomological Brauer groups in the context of complex-analytic spaces. The main result is that equality holds under…

Algebraic Geometry · Mathematics 2007-05-23 Stefan Schroeer

A new approach to \'etale homotopy theory is presented which applies to a much broader class of objects than previously existing approaches, namely it applies not only to all schemes (without any local Noetherian hypothesis), but also to…

Algebraic Geometry · Mathematics 2016-07-27 David Carchedi

We use the recently introduced \'etale open topology to prove several facts about large fields. We show that these facts lift to a very general topological setting.

Algebraic Geometry · Mathematics 2021-03-12 Erik Walsberg

We develop a theory of log adic spaces by combining the theories of adic spaces and log schemes, and study the Kummer \'etale and pro-Kummer \'etale topology for such spaces. We also establish the primitive comparison theorem in this…

Algebraic Geometry · Mathematics 2022-11-01 Hansheng Diao , Kai-Wen Lan , Ruochuan Liu , Xinwen Zhu

This is a survey of the recent development of the study of topological full groups of etale groupoids on the Cantor set. Etale groupoids arise from dynamical systems, e.g. actions of countable discrete groups, equivalence relations. Minimal…

Operator Algebras · Mathematics 2016-03-11 Hiroki Matui

We introduce so-called cone topologies of paratopological groups, which are a wide way to construct counterexamples, especially of examples of compact-like paratopological groups with discontinuous inversion. We found a simple interplay…

Group Theory · Mathematics 2019-08-08 Alex Ravsky

We define a fundamental group for digital images. Namely, we construct a functor from digital images to groups, which closely resembles the ordinary fundamental group from algebraic topology. Our construction differs in several basic ways…

Algebraic Topology · Mathematics 2019-06-17 Gregory Lupton , John Oprea , Nicholas Scoville

We introduce an abstract topos-theoretic framework for building Galois-type theories in a variety of different mathematical contexts; such theories are obtained from representations of certain atomic two-valued toposes as toposes of…

Category Theory · Mathematics 2013-01-03 Olivia Caramello

For almost finite groupoids, we study how their homology groups reflect dynamical properties of their topological full groups. It is shown that two clopen subsets of the unit space has the same class in H_0 if and only if there exists an…

Operator Algebras · Mathematics 2014-02-26 Hiroki Matui

In this paper, using the classical covering theory, we introduce a generalization of covering maps of a space $X$ with respect to a topology $\tau$ on the fundamental group of $X$. We show that the famous notions, covering, semicovering,…

Algebraic Topology · Mathematics 2026-02-24 Naghme Shahami , Behrooz Mashayekhy

We introduce a notion of a filtered model structure and use this notion to produce various model structures on pro-categories. This framework generalizes several known examples. We give several examples, including a homotopy theory for…

Algebraic Topology · Mathematics 2007-05-23 Halvard Fausk , Daniel C. Isaksen

Given a projective family of semi-stable curves over a complete discrete valuation ring of characteristic p with algebraically closed residue field, we construct a specialization functor between the category of continuous representations of…

Algebraic Geometry · Mathematics 2018-06-25 Elena Lavanda

We define the fundamental group underlying to Lichtenbaum's Weil-\'etale cohomology for number rings. To this aim, we define the Weil-\'etale topos as a refinement of the Weil-\'etale sites introduced in \cite{Lichtenbaum}. We show that the…

Number Theory · Mathematics 2010-10-01 Baptiste Morin

In this article, we develop the basic theory of digital topological groups. The basic definitions directly lead to two separate categories, based on the details of the continuity required of the group multiplication. We define $\NP_1$- and…

Computer Vision and Pattern Recognition · Computer Science 2022-08-24 Dae-Woong Lee , P. Christopher Staecker

In this paper, we explore a notion of nonabelian Hodge structure on the fundamental group of an algebraic variety. This is approach is compared to some alternative approaches due to Morgan, Hain and others. We also give criteria for a…

Algebraic Geometry · Mathematics 2009-08-06 Donu Arapura

In this paper we will give the computation of the etale fundamental group of an arithmetic scheme.

Algebraic Geometry · Mathematics 2009-12-21 Feng-Wen An

We present a diagram surveying equivalence or strict implication for properties of different nature (algebraic, model theoretic, topological, etc.) about groups definable in o-minimal structures. All results are well-known and an extensive…

Logic · Mathematics 2020-10-29 Annalisa Conversano

The topological fundamental group $\pi_{1}^{top}$ is a homotopy invariant finer than the usual fundamental group. It assigns to each space a quasitopological group and is discrete on spaces which admit universal covers. For an arbitrary…

Algebraic Topology · Mathematics 2020-04-14 Jeremy Brazas

We state a conjecture relating de Rham cohomology of a smooth rigid analytic variety to its compactly supported pro-\'etale cohomology. We prove the conjecture in the cases where the variety is a Stein curve of dimension one or a Stein…

Algebraic Geometry · Mathematics 2025-11-21 Sally Gilles