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We study stratification, that is the classification of localizing tensor ideal subcategories by geometric means, in the context of Kasparov's equivariant KK-theory of C*-algebras. We introduce a straightforward countable analog of the…

K-Theory and Homology · Mathematics 2026-01-21 Ivo Dell'Ambrogio , Rubén Martos

We study categories of matrix factorizations. These categories are defined for any regular function on a suitable regular scheme. Our paper has two parts. In the first part we develop the foundations; for example we discuss derived direct…

Algebraic Geometry · Mathematics 2013-10-25 Valery A. Lunts , Olaf M. Schnürer

We construct a modular functor which takes its values in the monoidal bicategory of finite categories, left exact functors and natural transformations. The modular functor is defined on bordisms that are 2-framed. Accordingly we do not need…

Quantum Algebra · Mathematics 2022-03-24 Jürgen Fuchs , Gregor Schaumann , Christoph Schweigert

We present a unified categorical framework that connects the syntactic Henkin construction for the first-order Completeness Theorem with Lawvere's Fixed-Point Theorem. Concretely, we define two canonical functors from the category of…

General Mathematics · Mathematics 2025-05-19 Barreto Joaquim Reizi

In this paper, we analyse the global dimension of the category of rational incomplete Mackey functors over a finite abelian group. Incomplete Mackey functors have recently risen to prominence in algebraic topology and hence it is valuable…

Algebraic Topology · Mathematics 2026-05-06 David Barnes , Anna Marie Bohmann , Michael A. Hill , Magdalena Kędziorek

As already mentioned by Lawvere in his 1973 paper, the characterisation of Cauchy completeness of metric spaces in terms of representability of adjoint distributors amounts to the idempotent-split property of an ordinary category when the…

Category Theory · Mathematics 2025-10-02 Dirk Hofmann , Walter Tholen

We introduce the notion of a matched pair of fusion rings and fusion categories, generalizing the one for groups. Using this concept, we define the bicrossed product of fusion rings and fusion categories and we construct exact…

Quantum Algebra · Mathematics 2025-07-09 Monique Müller , Héctor Martín Peña Pollastri , Julia Plavnik

A folklore result in category theory is that a (weakly) Cartesian closed category with finite co-products is distributive. Usually, the proof of this small result is carried on using the fact that the exponential functor is right adjoint to…

Category Theory · Mathematics 2014-06-16 Marco Benini

It is known that the construction of the frame of ideals from a distributive lattice induces a monad whose algebras are precisely the frames and frame homomorphisms. Using the Fakir construction of an idempotent approximation of a monad, we…

Category Theory · Mathematics 2024-05-01 Ando Razafindrakoto

Based on Gandy's principles for models of computation we give category-theoretic axioms describing locally deterministic updates to finite objects. Rather than fixing a particular category of states, we describe what properties such a…

Discrete Mathematics · Computer Science 2019-04-24 Joseph Razavi , Andrea Schalk

We prove that commutative semirings in a cartesian closed presentable $\infty$-category, as defined by Groth, Gepner, and Nikolaus, are equivalent to product-preserving functors from the $(2,1)$-category of bispans of finite sets. In other…

Category Theory · Mathematics 2025-05-09 Bastiaan Cnossen , Rune Haugseng , Tobias Lenz , Sil Linskens

In equivariant algebra, Mackey functors replace abelian groups and incomplete Tambara functors replace commutative rings. In this context, we prove that equivariant Hochschild homology can sometimes be computed using Mackey functor-valued…

Algebraic Topology · Mathematics 2024-07-29 David Mehrle , J. D. Quigley , Michael Stahlhauer

We resolve a conjecture of Cooper-Fenner-Purewal that a certain sequence of combinatorial matrices which can be used to bound small product-Ramsey numbers is positive semidefinite. Because the connection to Ramsey Theory involves solving…

Combinatorics · Mathematics 2017-05-01 Joshua Cooper , Maxwell Forst

The paper defines polynomials in a bicategory $\mathscr{M}$. Polynomials in bicategories $\mathrm{Spn}\mathscr{C} \ $ of spans in a finitely complete category $\mathscr{C} \ $ agree with polynomials in $\mathscr{C} \ $ as defined by Nicola…

Category Theory · Mathematics 2020-02-18 Ross Street

In general, all constructions of algebraic topology are functorial; the notions of category, functor and natural transformation originated here. The arrow categories are more simple forms of the \emph{comma} categories and were introduced…

General Mathematics · Mathematics 2024-06-26 Zoran Majkic

We provide a categorical proof of convergence for martingales and backward martingales in mean, using enriched category theory. The enrichment we use is in topological spaces, with their canonical closed monoidal structure, which encodes a…

Category Theory · Mathematics 2026-02-16 Paolo Perrone , Ruben Van Belle

We establish natural splittings for the values of global Mackey functors at orthogonal, unitary and symplectic groups. In particular, the restriction homomorphisms between the orthogonal, unitary and symplectic groups of adjacent dimensions…

Algebraic Topology · Mathematics 2022-08-09 Stefan Schwede

We develop the fundamentals of Mackey functors in the setup of fusion systems including an acyclicity condition as well as a parametrization and an explicit description of simple Mackey functors. Using this machinery we extend Dwyer's…

Algebraic Topology · Mathematics 2014-12-02 Antonio Díaz , Sejong Park

Suppose $G$ is a finite group. In this paper, we construct an equivalence between the $\infty$-category of algebras over an $N_{\infty}$-operad $\mathcal{O}$ associated to a $G$-indexing system $\mathcal{I}$ and the corresponding…

Algebraic Topology · Mathematics 2026-04-03 Gregoire Marc

Symmetric cohomology of groups, defined by M. Staic in [2], is similar to the way one defines the cyclic cohomology for algebras. We show that there is a well-defined restriction, conjugation and transfer map in symmetric cohomology, which…

Group Theory · Mathematics 2014-12-08 C. C. Todea