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In order to study the problems of extending an action along a quotient of the acted object and along a quotient of the acting object, we investigate some properties of the fibration of points. In fact, we obtain a characterization of…

Category Theory · Mathematics 2016-03-29 Giuseppe Metere

We develop parametrized generalizations of a number of fundamental concepts in the theory of $\infty$-categories, including factorization systems, free fibrations, exponentiable fibrations, relative colimits and relative Kan extensions,…

Category Theory · Mathematics 2022-01-11 Jay Shah

In this paper, we develop the theory for classifying all the geometric fibrations of compact, connected, flat $n$-orbifolds, over a 1-orbifold, up to affine equivalence. We apply our classification theory to classify all the geometric…

Geometric Topology · Mathematics 2020-05-08 John G. Ratcliffe , Steven T. Tschantz

A standard result from the theory of Grothendieck fibrations states that if $p : E \to B$ is a fibration, then $E$ has limits of shape $\mathcal{J}$ if $B$ has limits of shape $\mathcal{J}$ the fibers of $\mathcal{E}$ have limits of shape…

Category Theory · Mathematics 2025-09-08 Patrick Nicodemus

This paper is a continuation of our previous paper, Co-Seifert fibrations of compact flat orbifolds, in which we developed the theory for classifying geometric fibrations of compact, connected, flat $n$-orbifolds, over a 1-orbifold, up to…

Geometric Topology · Mathematics 2020-03-10 John G. Ratcliffe , Steven T. Tschantz

We revise the notion of the quasi-sectorial contractions. Our main theorem establishes a relation between semigroups of quasi-sectorial contractions and a class of m-sectorial generators. We discuss a relevance of this kind of contractions…

Functional Analysis · Mathematics 2007-11-06 V. A. Zagrebnov

Dimitri Ara's 2-quasi-categories, which are certain presheaves over Andr\'{e} Joyal's 2-cell category $\Theta_2$, are an example of a concrete model that realises the abstract notion of $(\infty,2)$-category. In this paper, we prove that…

Category Theory · Mathematics 2020-03-26 Yuki Maehara

This paper gives an introduction to the homotopy theory of quasi-categories. Weak equivalences between quasi-categories are characterized as maps which induce equivalences on a naturally defined system of groupoids. These groupoids…

Category Theory · Mathematics 2019-09-19 J. F. Jardine

Let $R$ be a commutative ring with unit. We consider the homotopy theory of the category of spectral sequences of $R$-modules with the class of weak equivalences given by those morphisms inducing a quasi-isomorphism at a certain fixed page.…

Algebraic Topology · Mathematics 2023-02-22 Muriel Livernet , Sarah Whitehouse

In this note we define fibrations of topological stacks and establish their main properties. We prove various standard results about fibrations (fiber homotopy exact sequence, Leray-Serre and Eilenberg-Moore spectral sequences, etc.). We…

Algebraic Topology · Mathematics 2010-10-11 Behrang Noohi

We generalize the small object argument in order to allow for its application to proper classes of maps (as opposed to sets of maps in Quillen's small object argument). The necessity of such a generalization arose with appearance of several…

Algebraic Topology · Mathematics 2007-05-23 Boris Chorny

The set of quasipositive surfaces is closed under incompressible inclusion. We prove that the induced order on fibre surfaces of positive braid links is almost a well-quasi-order. When restricting to quasipositive surfaces containing a…

Geometric Topology · Mathematics 2021-04-26 Sebastian Baader , Pierre Dehornoy , Livio Liechti

Using full images of accessible functors, we prove some results about combinatorial and accessible model categories. In particular, we give an example of a weak factorization system on a locally presentable category which is not accessible.

Category Theory · Mathematics 2022-02-08 Jiří Rosický

We classify exterior fibrations in the exterior homotopy category. As a result we also classify proper fibrations between CW-complexes.

Algebraic Topology · Mathematics 2019-06-05 Jose Manuel García-Calcines , Pedro Ruymán García-Díaz , Aniceto Murillo

We construct a left semi-model structure on the category of intensional type theories (precisely, on $\mathrm{CxlCat_{Id,1,\Sigma(,\Pi_{ext})}}$). This presents an $\infty$-category of such type theories; we show moreover that there is an…

Category Theory · Mathematics 2026-02-06 Chris Kapulkin , Peter LeFanu Lumsdaine

We use Cisinski's machinery to construct and study model structures on the category of simplicial sets whose classes of fibrant objects generalize quasi-categories. We identify a lifting condition which captures the homotopical behavior of…

Algebraic Topology · Mathematics 2025-04-02 Matthew Feller

We construct a model structure on the category of cubical sets with connections whose cofibrations are the monomorphisms and whose fibrant objects are defined by the right lifting property with respect to inner open boxes, the cubical…

Algebraic Topology · Mathematics 2022-02-08 Brandon Doherty , Chris Kapulkin , Zachery Lindsey , Christian Sattler

A generalization of the notion of an $\infty$-category is presented, allowing for ($\infty$-)cat(egorie)s that may have non-invertible higher morphisms.

Category Theory · Mathematics 2014-03-10 Daniel Gerigk

We prove that the $\infty$-category of orthogonal factorization systems embeds fully faithfully into the $\infty$-category of double $\infty$-categories. Moreover, we prove an (un)straightening equivalence for double $\infty$-categories,…

Category Theory · Mathematics 2025-01-03 Branko Juran

We investigate classifications of quasitrivial semigroups defined by certain equivalence relations. The subclass of quasitrivial semigroups that preserve a given total ordering is also investigated. In the special case of finite semigroups,…

Rings and Algebras · Mathematics 2020-05-21 Jimmy Devillet , Jean-Luc Marichal , Bruno Teheux