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Our work over the past years shows that not only the collection of (for instance) all topological spaces gives rise to a category, but also each topological space can be seen individually as a category by interpreting the convergence…

Category Theory · Mathematics 2008-04-03 Dirk Hofmann

We introduce two novel complementary notions of the Lefschetz number for a functor from a finite acyclic category to itself and we prove a Lefschetz fixed-object theorem and a Lefschetz fixed-morphism theorem. In order to do so, we use the…

Algebraic Topology · Mathematics 2024-04-11 Samuel Castelo-Mourelle , Enrique Macías-Virgós , David Mosquera-Lois

A notion of a coring extension is defined and it is related to the existence of an additive functor between comodule categories that factorises through forgetful functors. This correspondence between coring extensions and factorisable…

Rings and Algebras · Mathematics 2008-07-31 Tomasz Brzezinski

The postulates of comprehension and extensionality in set theory are based on an inversion principle connecting set-theoretic abstraction and the property of having a member. An exactly analogous inversion principle connects functional…

Category Theory · Mathematics 2007-05-23 K. Dosen

The main result of this paper utilizes the representation graph of a group $G$, $R(V,G)$, and gives a general construction of a diagrammatic category $\mathbf{Dgrams}_{R(V,G)}$. The proof of the main theorem shows that, given explicit…

Category Theory · Mathematics 2025-02-10 Ryan Reynolds

We establish a criterion for determining when a family of geometric functors is jointly conservative through the lens of purity in compactly generated triangulated categories. We introduce the notion of pure descendability and we apply it…

Algebraic Topology · Mathematics 2026-02-17 Natàlia Castellana , Juan Omar Gómez

Let E be a (right) Hilbert C*-module over a C*-algebra A. If E is equipped with a left action of a second C*-algebra B, then tensor product with E gives rise to a functor from the category of Hilbert B-modules to the category of Hilbert…

Operator Algebras · Mathematics 2016-07-06 Pierre Clare , Tyrone Crisp , Nigel Higson

We show that differential calculus (in its usual form, or in the general form of topological differential calculus) can be fully imdedded into a functor category (functors from a small category of anchord tangent algebras to anchored sets).…

Algebraic Geometry · Mathematics 2021-03-25 Wolfgang Bertram , Jérémy Haut

We demonstrate that companionships and conjunctions in double $\infty$-categories -- and more generally, in double Segal spaces -- extend to functors out of the free-living companionship and conjunction respectively. Specifically, we prove…

Category Theory · Mathematics 2025-04-09 Jaco Ruit

We introduce and develop the notion of *displayed categories*. A displayed category over a category C is equivalent to "a category D and functor F : D --> C", but instead of having a single collection of "objects of D" with a map to the…

Category Theory · Mathematics 2023-06-22 Benedikt Ahrens , Peter LeFanu Lumsdaine

We characterize virtual double categories of enriched categories, functors, and profunctors by introducing a new notion of double-categorical colimits. Our characterization is strict in the sense that it is up to equivalence between virtual…

Category Theory · Mathematics 2026-04-07 Yuto Kawase

We introduce a graphical language for closed symmetric monoidal categories based on an extension of string diagrams with special bracket wires representing internal homs. These bracket wires make the structure of the internal hom functor…

Logic in Computer Science · Computer Science 2025-12-09 Callum Reader , Alessandro Di Giorgio

Associating graph algebras to directed graphs leads to both covariant and contravariant functors from suitable categories of graphs to the category k-Alg of algebras and algebra homomorphisms. As both functors are often used at the same…

Rings and Algebras · Mathematics 2026-04-30 Gilles G. de Castro , Francesco D'Andrea , Piotr M. Hajac

Nested conditions are used, among other things, as a graphical way to express first order formulas ruling the applicability of a graph transformation rule to a given match. In this paper, we propose (for the first time) a notion of…

Logic in Computer Science · Computer Science 2024-08-13 Arend Rensink , Andrea Corradini

Relative theories(=closed subfunctors) are considered in exact, triangulated and extriangulated categories by Dr\"{a}xler-Reiten-Smal{\o}-Solberg-Keller, Beligiannis and Herschend-Liu-Nakaoka, respectively. We give a construction method of…

Category Theory · Mathematics 2021-11-30 Arashi Sakai

We investigate Riguet congruences and generalized congruences on a category, focusing on their interrelations from both lattice-theoretic and category-theoretic perspectives. We also characterize functors that are full and surjective on…

Category Theory · Mathematics 2026-05-21 Juan Climent Vidal , Enric Cosme Llópez , Raúl Ruiz Mora

We prove that there is an adjunction between what we call \'etale topological categories and restriction quantal frames that leads to an adjunction with a category of complete restriction monoids. This generalizes the adjunction between…

Category Theory · Mathematics 2023-03-10 Mark V. Lawson

We specialise a recently introduced notion of generalised dinaturality for functors $T : (\mathcal{C}^\text{op})^p \times \mathcal{C}^q \to \mathcal{D}$ to the case where the domain (resp., codomain) is constant, obtaining notions of ends…

Category Theory · Mathematics 2023-03-03 Fosco Loregian , Emily de Oliveira Santos

These notes are meant to provide a rapid introduction to triangulated categories. We start with the definition of an additive category and end with a glimps of tilting theory. Some exercises are included.

K-Theory and Homology · Mathematics 2007-05-23 Behrang Noohi

We show that the category of categories with pullbacks and pullback preserving functors is cartesian closed.

Category Theory · Mathematics 2009-04-17 John Bourke
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