Day Convolution for Monoidal Bicategories
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Profunctors in Mal'cev Categories and Fractions of Functors
PROFUNCTORS IN MALTCEV CATEGORIES AND FRACTIONS OF FUNCTORS S. MANTOVANI, G. METERE, E. M. VITALE ABSTRACT. We study internal profunctors and their normalization under various conditions on the base category. In the Maltcev case we give an easy characterization of profunctors. Moreover, when the base category is efficiently regular, we characterize those profunctors which are fractions of internal functors with respect to weak equiva- lences. 1. Introduction In this paper we study internal profunctors in a category C; from diverse points of view. We start by analyzing their very definition in the case C is Maltcev. It is well known that the algebraic constraints inherited by the Maltcev condition make internal categorical constructions often easier to deal with. For instance, internal cate- gories are groupoids, and their morphisms are just morphisms of the underlying reflective graphs. Along these lines, internal profunctors, that generalize internal functors are in- volved in a similar phenomenon: it turns out (Proposition 3.1) that in Maltcev categories one of the axioms defining internal profunctors can be obtained by the others. Our interest in studying internal profunctors in this context, comes from an attempt to describe internally monoidal functors of 2-groups as weak morphisms of internal groupoids. In the case of groups, the problem has been solved by introducing the notion of butterfly by B. Noohi in [22] (see also [2] for a stack version). In [1] an internal version of butterflies has been defined in a semi-abelian context, and it has been proved that they give rise to the bicategory of fractions of Grpd(C) (the 2-category of internal groupoids and internal functors) with respect to weak equivalences. -
The Hecke Bicategory
Axioms 2012, 1, 291-323; doi:10.3390/axioms1030291 OPEN ACCESS axioms ISSN 2075-1680 www.mdpi.com/journal/axioms Communication The Hecke Bicategory Alexander E. Hoffnung Department of Mathematics, Temple University, 1805 N. Broad Street, Philadelphia, PA 19122, USA; E-Mail: [email protected]; Tel.: +215-204-7841; Fax: +215-204-6433 Received: 19 July 2012; in revised form: 4 September 2012 / Accepted: 5 September 2012 / Published: 9 October 2012 Abstract: We present an application of the program of groupoidification leading up to a sketch of a categorification of the Hecke algebroid—the category of permutation representations of a finite group. As an immediate consequence, we obtain a categorification of the Hecke algebra. We suggest an explicit connection to new higher isomorphisms arising from incidence geometries, which are solutions of the Zamolodchikov tetrahedron equation. This paper is expository in style and is meant as a companion to Higher Dimensional Algebra VII: Groupoidification and an exploration of structures arising in the work in progress, Higher Dimensional Algebra VIII: The Hecke Bicategory, which introduces the Hecke bicategory in detail. Keywords: Hecke algebras; categorification; groupoidification; Yang–Baxter equations; Zamalodchikov tetrahedron equations; spans; enriched bicategories; buildings; incidence geometries 1. Introduction Categorification is, in part, the attempt to shed new light on familiar mathematical notions by replacing a set-theoretic interpretation with a category-theoretic analogue. Loosely speaking, categorification replaces sets, or more generally n-categories, with categories, or more generally (n + 1)-categories, and functions with functors. By replacing interesting equations by isomorphisms, or more generally equivalences, this process often brings to light a new layer of structure previously hidden from view. -
Epapyrus PDF Document
KyungpooJ‘ Math ]. Volume 18. Number 2 ,December. 1978 ON REFLECTIVE SUBCATEGORIES By Cho, Y ong-Seung Let α be a given fulI subcategory of '?!. Under what conditions does there ‘exist a smalIest, replete, reflective subcategory α* of '?! for which α* contains α? The answer to this question is unknown. Even if '?! is the category of uniform spaces and uniform maps, it is an open question. J. F. Kennison :answered to the above question partialIy, in case '?! is a complete category with a well-founded bicategory structure and α is a fulI, replete and closed under the formation of products (1]. In this paper, the author could construct a ’ smalIest, replete, reflective subcategory α* of '?! for which α육 contains α under 'other conditions except the fact that α is full. Throughout this paper, our definitions and notations are based on ((1] , (5] , [6] , [10] , [11]). The class of all epimorphisms of '?! will be denoted by Efr and M '6' the class of alI monomorphisms of '?!. DEFINITION. Let '?! be a category and let 1 and P be classes of morphisms 'on '?!. Then (I, P) is a bz'category structure on '?! provided that: B-l) Every isomorphism is in Inp. B-2) [ and P are closed under the composition of morphisms. B-3) Every morphism 1 can be factored as 1=지 lowith 11 ε 1 and 1。, εP. Moreover this factorization is unique to within an isomorphism in the sense that if I=gh and gε 1 and hEP then there exists an isomorphism e for which ,elo= 1z and ge=/1• B-4) PCE B-5) ICM DEFINITION. -
Coherence for Braided and Symmetric Pseudomonoids
Coherence for braided and symmetric pseudomonoids Dominic Verdon School of Mathematics, University of Bristol December 4, 2018 Abstract Computads for unbraided, braided, and symmetric pseudomonoids in semistrict monoidal bicategories are defined. Biequivalences characterising the monoidal bicategories generated by these computads are proven. It is shown that these biequivalences categorify results in the theory of monoids and commutative monoids, and generalise the standard coher- ence theorems for braided and symmetric monoidal categories to braided and symmetric pseudomonoids in any weak monoidal bicategory. 1 Introduction 1.1 Overview Braided and symmetric pseudomonoids. Naked, braided and symmetric pseudomonoids are categorifications of noncommutative and commutative monoids, obtained by replacing equal- ity with coherent isomorphism. In the symmetric monoidal bicategory Cat of categories, func- tors and natural transformations, such structures are precisely naked, braided and symmetric monoidal categories. Naked, braided and symmetric pseudomonoids are more general, however, as they can be defined in any monoidal bicategory with the requisite braided structure [30]. Pseudomonoids in braided and symmetric monoidal bicategories arise in a variety of mathe- matical settings. By categorification of the representation theory of Hopf algebras, bicategories encoding the data of a four-dimensional topological field theory can be obtained as represen- tation categories of certain `Hopf' pseudomonoids [32, 8]. Pseudomonoids have also appeared recently in the the theory of surface foams, where certain pseudomonoids in a braided monoidal category represent knotted foams in four-dimensional space [7]. Many properties of monoidal categories can be formulated externally as structures on pseudomonoids; for instance, Street showed that Frobenius pseudomonoids correspond to star-autonomous categories [36], giving rise to a diagrammatic calculus for linear logic [13]. -
Profunctors, Open Maps and Bisimulation
BRICS RS-04-22 Cattani & Winskel: Profunctors, Open Maps and Bisimulation BRICS Basic Research in Computer Science Profunctors, Open Maps and Bisimulation Gian Luca Cattani Glynn Winskel BRICS Report Series RS-04-22 ISSN 0909-0878 October 2004 Copyright c 2004, Gian Luca Cattani & Glynn Winskel. BRICS, Department of Computer Science University of Aarhus. All rights reserved. Reproduction of all or part of this work is permitted for educational or research use on condition that this copyright notice is included in any copy. See back inner page for a list of recent BRICS Report Series publications. Copies may be obtained by contacting: BRICS Department of Computer Science University of Aarhus Ny Munkegade, building 540 DK–8000 Aarhus C Denmark Telephone: +45 8942 3360 Telefax: +45 8942 3255 Internet: [email protected] BRICS publications are in general accessible through the World Wide Web and anonymous FTP through these URLs: http://www.brics.dk ftp://ftp.brics.dk This document in subdirectory RS/04/22/ Profunctors, Open Maps and Bisimulation∗ Gian Luca Cattani DS Data Systems S.p.A., Via Ugozzolo 121/A, I-43100 Parma, Italy. Email: [email protected]. Glynn Winskel University of Cambridge Computer Laboratory, Cambridge CB3 0FD, England. Email: [email protected]. October 2004 Abstract This paper studies fundamental connections between profunctors (i.e., dis- tributors, or bimodules), open maps and bisimulation. In particular, it proves that a colimit preserving functor between presheaf categories (corresponding to a profunctor) preserves open maps and open map bisimulation. Consequently, the composition of profunctors preserves open maps as 2-cells. -
The Low-Dimensional Structures Formed by Tricategories
Math. Proc. Camb. Phil. Soc. (2009), 146, 551 c 2009 Cambridge Philosophical Society 551 doi:10.1017/S0305004108002132 Printed in the United Kingdom First published online 28 January 2009 The low-dimensional structures formed by tricategories BY RICHARD GARNER Department of Mathematics, Uppsala University, Box 480,S-751 06 Uppsala, Sweden. e-mail: [email protected] AND NICK GURSKI Department of Mathematics, Yale University, 10 Hillhouse Avenue, PO Box 208283, New Haven, CT 06520-8283, U.S.A. e-mail: [email protected] (Received 15 November 2007; revised 2 September 2008) Abstract We form tricategories and the homomorphisms between them into a bicategory, whose 2-cells are certain degenerate tritransformations. We then enrich this bicategory into an ex- ample of a three-dimensional structure called a locally cubical bicategory, this being a bic- ategory enriched in the monoidal 2-category of pseudo double categories. Finally, we show that every sufficiently well-behaved locally cubical bicategory gives rise to a tricategory, and thereby deduce the existence of a tricategory of tricategories. 1. Introduction A major impetus behind many developments in 2-dimensional category theory has been the observation that, just as the fundamental concepts of set theory are categorical in nature, so the fundamental concepts of category theory are 2-categorical in nature. In other words, if one wishes to study categories “in the small” – as mathematical entities in their own right rather than as universes of discourse – then a profitable way of doing this is by studying the 2-categorical properties of Cat, the 2-category of all categories.1 Once one moves from the study of categories to the study of (possibly weak) n-categories, it is very natural to generalise the above maxim, and to assert that the fundamental concepts of n-category theory are (n + 1)-categorical in nature. -
The Periodic Table of N-Categories for Low Dimensions I: Degenerate Categories and Degenerate Bicategories Draft
The periodic table of n-categories for low dimensions I: degenerate categories and degenerate bicategories draft Eugenia Cheng and Nick Gurski Department of Mathematics University of Chicago E-mail: [email protected], [email protected] July 2005 Abstract We examine the periodic table of weak n-categories for the low-dimensional cases. It is widely understood that degenerate categories give rise to monoids, doubly degenerate bicategories to commutative monoids, and degenerate bicategories to monoidal categories; however, to understand this correspondence fully we examine the totalities of such structures to- gether with maps between them and higher maps between those. Cate- gories naturally form a 2-category Cat so we take the full sub-2-category of this whose 0-cells are the degenerate categories. Monoids naturally form a category, but we regard this as a discrete 2-category to make the comparison. We show that this construction does not yield a biequiva- lence; to get an equivalence we ignore the natural transformations and consider only the category of degenerate categories. A similar situation occurs for degenerate bicategories. The tricategory of such does not yield an equivalence with monoidal categories; we must consider only the cate- gories of such structures. For doubly degenerate bicategories the tricate- gory of such is not naturally triequivalent to the category of commutative monoids (regarded as a tricategory). However in this case considering just the categories does not give an equivalence either; to get an equivalence we consider the bicategory of doubly degenerate bicategories. We conclude with a hypothesis about how the above cases might generalise for n-fold degenerate n-categories. -
Constructing Symmetric Monoidal Bicategories Functorially
Constructing symmetric monoidal bicategories. functorially Constructing symmetric monoidal bicategories functorially Michael Shulman Linde Wester Hansen AMS Sectional Meeting UC Riverside Applied Category Theory Special Session November 9, 2019 Constructing symmetric monoidal bicategories. functorially Outline 1 Constructing symmetric monoidal bicategories. 2 . functorially Constructing symmetric monoidal bicategories. functorially Symmetric monoidal bicategories Symmetric monoidal bicategories are everywhere! 1 Rings and bimodules 2 Sets and spans 3 Sets and relations 4 Categories and profunctors 5 Manifolds and cobordisms 6 Topological spaces and parametrized spectra 7 Sets and (decorated/structured) cospans 8 Sets and open Markov processes 9 Vector spaces and linear relations Constructing symmetric monoidal bicategories. functorially What is a symmetric monoidal bicategory? A symmetric monoidal bicategory is a bicategory B with 1 A functor ⊗: B × B ! B 2 A pseudonatural equivalence (A ⊗ B) ⊗ C ' A ⊗ (B ⊗ C) 3 An invertible modification ((AB)C)D (A(BC))D A((BC)D) π + (AB)(CD) A(B(CD)) 4 = 5 more data and axioms for units, braiding, syllepsis. Constructing symmetric monoidal bicategories. functorially Surely it can't be that bad In all the examples I listed before, the monoidal structures 1 tensor product of rings 2 cartesian product of sets 3 cartesian product of spaces 4 disjoint union of sets 5 ... are actually associative up to isomorphism, with strictly commuting pentagons, etc. But a bicategory doesn't know how to talk about isomorphisms, only equivalences! We need to add extra data: ring homomorphisms, functions, linear maps, etc. Constructing symmetric monoidal bicategories. functorially Double categories A double category is an internal category in Cat. It has: 1 objects A; B; C;::: 2 loose morphisms A −7−! B that compose weakly 3 tight morphisms A ! B that compose strictly 4 2-cells shaped like squares: A j / B : + C j / D No one can agree on which morphisms to draw horizontally or vertically. -
Exercise Sheet
Exercises on Higher Categories Paolo Capriotti and Nicolai Kraus Midlands Graduate School, April 2017 Our course should be seen as a very first introduction to the idea of higher categories. This exercise sheet is a guide for the topics that we discuss in our four lectures, and some exercises simply consist of recalling or making precise concepts and constructions discussed in the lectures. The notion of a higher category is not one which has a single clean def- inition. There are numerous different approaches, of which we can only discuss a tiny fraction. In general, a very good reference is the nLab at https://ncatlab.org/nlab/show/HomePage. Apart from that, a very incomplete list for suggested further reading is the following (all available online). For an overview over many approaches: – Eugenia Cheng and Aaron Lauda, Higher-Dimensional Categories: an illustrated guide book available online, cheng.staff.shef.ac.uk/guidebook Introductions to simplicial sets: – Greg Friedman, An Elementary Illustrated Introduction to Simplicial Sets very gentle introduction, arXiv:0809.4221. – Emily Riehl, A Leisurely Introduction to Simplicial Sets a slightly more advanced introduction, www.math.jhu.edu/~eriehl/ssets.pdf Quasicategories: – Jacob Lurie, Higher Topos Theory available as paperback (ISBN-10: 0691140499) and online, arXiv:math/0608040 Operads (not discussed in our lectures): – Tom Leinster, Higher Operads, Higher Categories available as paperback (ISBN-10: 0521532159) and online, 1 arXiv:math/0305049 Note: Exercises are ordered by topic and can be done in any order, unless an exercise explicitly refers to a previous one. We recommend to do the exercises marked with an arrow ⇒ first. -
A Whirlwind Tour of the World of (∞,1)-Categories
Contemporary Mathematics A Whirlwind Tour of the World of (1; 1)-categories Omar Antol´ınCamarena Abstract. This introduction to higher category theory is intended to a give the reader an intuition for what (1; 1)-categories are, when they are an appro- priate tool, how they fit into the landscape of higher category, how concepts from ordinary category theory generalize to this new setting, and what uses people have put the theory to. It is a rough guide to a vast terrain, focuses on ideas and motivation, omits almost all proofs and technical details, and provides many references. Contents 1. Introduction 2 2. The idea of higher category theory 3 2.1. The homotopy hypothesis and the problem with strictness 5 2.2. The 3-type of S2 8 2.3. Shapes for cells 10 2.4. What does (higher) category theory do for us? 11 3. Models of (1; 1)-categories 12 3.1. Topological or simplicial categories 12 3.2. Quasi-categories 13 3.3. Segal categories and complete Segal spaces 16 3.4. Relative categories 17 3.5. A1-categories 18 3.6. Models of subclasses of (1; 1)-categories 20 3.6.1. Model categories 20 3.6.2. Derivators 21 3.6.3. dg-categories, A1-categories 22 4. The comparison problem 22 4.1. Axiomatization 24 5. Basic (1; 1)-category theory 25 5.1. Equivalences 25 5.1.1. Further results for quasi-categories 26 5.2. Limits and colimits 26 5.3. Adjunctions, monads and comonads 28 2010 Mathematics Subject Classification. Primary 18-01. -
Ends and Coends
THIS IS THE (CO)END, MY ONLY (CO)FRIEND FOSCO LOREGIAN† Abstract. The present note is a recollection of the most striking and use- ful applications of co/end calculus. We put a considerable effort in making arguments and constructions rather explicit: after having given a series of preliminary definitions, we characterize co/ends as particular co/limits; then we derive a number of results directly from this characterization. The last sections discuss the most interesting examples where co/end calculus serves as a powerful abstract way to do explicit computations in diverse fields like Algebra, Algebraic Topology and Category Theory. The appendices serve to sketch a number of results in theories heavily relying on co/end calculus; the reader who dares to arrive at this point, being completely introduced to the mysteries of co/end fu, can regard basically every statement as a guided exercise. Contents Introduction. 1 1. Dinaturality, extranaturality, co/wedges. 3 2. Yoneda reduction, Kan extensions. 13 3. The nerve and realization paradigm. 16 4. Weighted limits 21 5. Profunctors. 27 6. Operads. 33 Appendix A. Promonoidal categories 39 Appendix B. Fourier transforms via coends. 40 References 41 Introduction. The purpose of this survey is to familiarize the reader with the so-called co/end calculus, gathering a series of examples of its application; the author would like to stress clearly, from the very beginning, that the material presented here makes arXiv:1501.02503v2 [math.CT] 9 Feb 2015 no claim of originality: indeed, we put a special care in acknowledging carefully, where possible, each of the many authors whose work was an indispensable source in compiling this note. -
Arxiv:2011.12106V1 [Math.AT] 24 Nov 2020 Over the Graded Ring E∗ := Π∗(E)
FLAT REPLACEMENTS OF HOMOLOGY THEORIES DANIEL SCHÄPPI Abstract. To a homology theory one can associate an additive site and a new homological functor with values in the category of additive sheaves on that site. If this category of sheaves can be shown to be equivalent to a category of comodules of a Hopf algebroid, then we obtain a new homology theory by composing with the underlying module functor. This new homology theory is always flat and we call it a flat replacement of the original theory. For example, Pstrągowski has shown that complex cobordism is a flat replacement of singular homology. In this article we study the basic properties of the sites associated to homology theories and we prove an existence theorem for flat replacements. Contents 1. Introduction 1 Acknowledgements 3 2. Grothendieck tensor categories associated to homology theories 3 2.1. Coefficient categories 3 2.2. The additive site of a homology theory 12 2.3. Flat replacements 17 3. Locally free objects 24 3.1. Preliminaries 24 3.2. Recollections about Adams algebras 25 3.3. Recognizing locally free objects 27 4. Examples of homology theories with flat replacements 32 4.1. Detecting duals 32 4.2. Existence of flat replacements 36 4.3. Locally free objects in module categories 41 References 44 1. Introduction Let SH denote the stable homotopy category. If E is a commutative ring object in SH, then E∗X := π∗(E^X) defines a homological functor with values in modules arXiv:2011.12106v1 [math.AT] 24 Nov 2020 over the graded ring E∗ := π∗(E).