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We provide a generalized treatment of (co)cartesian arrows, fibrations, and functors. Compared to the classical conditions, the endpoint inclusions get replaced by arbitrary shape inclusions. Our framework is Riehl--Shulman's simplicial…

Category Theory · Mathematics 2024-03-14 Jonathan Weinberger

In an abelian category, the (bi)fibration of subobjects is isomorphic to the (bi)fibration of quotients. This property captures substantial information about the exactness structure of a category. Indeed, as it was shown by the second…

Category Theory · Mathematics 2025-10-13 Elena Caviglia , Zurab Janelidze , Luca Mesiti

We give a new criterion guaranteeing existence of model structures left-induced along a functor admitting both adjoints. This works under the hypothesis that the functor induces idempotent adjunctions at the homotopy category level. As an…

Category Theory · Mathematics 2022-10-25 Philip Hackney , Martina Rovelli

We provide a bicategorical generalization of Barr's landmark 1970 paper, in which he describes how to extend Set-monads to relations and uses this to characterize topological spaces as the relational algebras of the ultrafilter monad. With…

Category Theory · Mathematics 2026-04-13 Quentin Aristote , Umberto Tarantino

Let $(\mathcal{A}, \mathcal{B}, \mathcal{C}, i^{*}, i_{\ast}, i^{!},j_!, j^\ast, j_\ast)$ be a recollement of extriangulated categories. We show that there is a bijection between thick subcategories in $\mathcal{C}$ and thick subcategories…

Representation Theory · Mathematics 2024-10-29 Yuxia Mei , Li Wang , Jiaqun Wei

We give an example of a morphism of simplicial sets which is a monomorphism, bijective on 0-simplices, and a weak categorical equivalence, but which is not inner anodyne. This answers an open question of Joyal. Furthermore, we use this…

Algebraic Topology · Mathematics 2019-10-22 Alexander Campbell

We categorify various Fock space representations on the algebra of symmetric functions via the category of polynomial functors. In a prequel, we used polynomial functors to categorify the Fock space representations of type A affine Lie…

Representation Theory · Mathematics 2015-04-07 Jiuzu Hong , Oded Yacobi

These are expanded lecture notes from lectures given at the Workshop on higher structures at MATRIX Melbourne. These notes give an introduction to Feynman categories and their applications. Feynman categories give a universal categorical…

Algebraic Topology · Mathematics 2017-06-02 Ralph M. Kaufmann

We propose a conjectural extension to positive characteristic case of a well known Deligne's theorem on the existence of super fiber functors. We prove our conjecture in the special case of semisimple categories with finitely many…

Category Theory · Mathematics 2015-03-06 Victor Ostrik

An n-truncated model structure on simplicial (pre-)sheaves is described having as weak equivalences maps that induce isomorphisms on certain homotopy sheaves only up to degree n. Starting from one of Jardine's intermediate model structures…

Algebraic Topology · Mathematics 2013-09-11 Georg Biedermann

The familiar construction of categories of fractions, due to Gabriel and Zisman, allows one to invert a class W of arrows in a category in a universal way. Similarly, bicategories of fractions allow one to invert a collection of arrows in a…

Category Theory · Mathematics 2013-03-05 Dorette A. Pronk , Michael A. Warren

In an abelian category $\mathscr{A}$ with small ${\rm Ext}$ groups, we show that there exists a one-to-one correspondence between any two of the following: balanced pairs, subfunctors $\mathcal{F}$ of ${\rm Ext}^{1}_{\mathscr{A}}(-,-)$ such…

Representation Theory · Mathematics 2015-10-27 Junfu Wang , Zhaoyong Huang

We provide a calculus of mates for functors to the $\infty$-category of $\infty$-categories and extend Lurie's unstraightening equivalences to show that (op)lax natural transformations correspond to maps of (co)cartesian fibrations that do…

Category Theory · Mathematics 2024-04-04 Rune Haugseng , Fabian Hebestreit , Sil Linskens , Joost Nuiten

A multifiltration is a functor indexed by $\mathbb{N}^r$ that maps any morphism to a monomorphism. The goal of this paper is to describe in an explicit and combinatorial way the natural $\mathbb{N}^r$-graded $R[x_1,\ldots, x_r]$-module…

Algebraic Topology · Mathematics 2014-09-30 Wojciech Chacholski , Martina Scolamiero , Francesco Vaccarino

Given a family of model categories $\cal E \to \cal C$, we associate to it a homotopical category of derived, or Segal, sections $DSect(\cal C,\cal E)$ that models the higher-categorical sections of the localisation $L\cal E \to \cal C$.…

Category Theory · Mathematics 2018-12-05 Edouard Balzin

(Pseudo) double categories have two sorts of morphisms: tight ones which compose strictly, and loose ones which compose up to coherent isomorphism. In this paper, we consider bimodules between double categories in the loose direction. We…

Category Theory · Mathematics 2025-10-29 Jason Brown , Kevin Carlson , Sophie Libkind , David Jaz Myers

We develop a theory of generalized Hopf invariants in the setting of sectional category. In particular we show how Hopf invariants for a product of fibrations can be identified as shuffle joins of Hopf invariants for the factors. Our…

Algebraic Topology · Mathematics 2017-07-18 Jesús González , Mark Grant , Lucile Vandembroucq

This paper gives a uniform-theoretic refinement of classical homotopy theory. Both cubical sets (with connections) and uniform spaces admit classes of weak equivalences, special cases of classical weak equivalences, appropriate for the…

Algebraic Topology · Mathematics 2021-09-20 Sanjeevi Krishnan , Crichton Ogle

We construct combinatorial model category structures on the categories of (marked) categories and (marked) pre-additive categories, and we characterize (marked) additive categories as fibrant objects in a Bousfield localization of…

Algebraic Topology · Mathematics 2021-05-28 Ulrich Bunke , Alexander Engel , Daniel Kasprowski , Christoph Winges

Consider a locally cartesian closed category with an object I and a class of trivial fibrations, which admit sections and are stable under pushforward and retract as arrows. Define the fibrations to be those maps whose Leibniz exponential…

Category Theory · Mathematics 2024-11-20 Sina Hazratpour , Emily Riehl