CyberSec Research

In this paper we describe a comma 2-comonad on the 2-category whose objects are functors, 1-cell are colax squares and 2-cells are their transformations. We give a complete description of the Eilenberg-Moore 2-category of colax coalgebras, colax morphisms between them and their transformations and we show how many fundamental constructions in formal category theory like adjoint triples, distributive laws, comprehension structures, Frobenius functors etc. naturally fit in this context.

If X is a groupoid equipped with an action of a 2-group G then one has a 2-groupoid X/G. We describe the fibers of the functor from X/G to the 1-groupoid $\pi_0(X)/\pi_0(G)$. We also give an explicit model for X/G in a certain situation.

Based on the intuitive notion of convexity, we formulate a universal property defining interval objects in a category with finite products. Interval objects are structures corresponding to closed intervals of the real line, but their definition does not assume a pre-existing notion of real number. The universal property characterises such structures up to isomorphism, supports the definition of functions between intervals, and provides a means of verifying identities between functions. In the category of sets, the universal property characterises closed intervals of real numbers with nonempty interior. In the the category of topological spaces, we obtain intervals with the Euclidean topology. We also prove that every elementary topos with natural numbers object contains an interval object; furthermore, we characterise interval objects as intervals of real numbers in the Cauchy completion of the rational numbers within the Dedekind reals.

Using the language of string diagrams, we define categorical generalizations of modules for map algebras $\mathfrak{g} \otimes A$ and equivariant map algebras $(\mathfrak{g} \otimes A)^\Gamma$, where $\mathfrak{g}$ is a Lie algebra, $A$ is a commutative associative algebra, and $\Gamma$ is an abelian group acting on $\mathfrak{g}$ and $A$. After establishing some properties of these modules, we present several examples of how our definitions can applied in various diagrammatic categories. In particular, we use the oriented Brauer category OB to construct a candidate interpolating category for the categories of $\mathfrak{gl}_n \otimes k[t]$-modules.

We show that the homotopy theory of monoidal relative categories is equivalent to that of monoidal $\infty$-categories, as well as its symmetric monoidal version. As an application, we give a concise and complete proof of the fact that every presentably monoidal or presentably symmetric monoidal $\infty$-category is presented by a monoidal or symmetric monoidal model category, which, in the monoidal case, was sketched by Lurie, and in the symmetric monoidal case, was proved by Nikolaus--Sagave.

A DR-semigroup $S$ (also known as a reduced E-semiabundant or reduced E-Fountain semigroup) is here viewed as a semigroup equipped with two unary operations $D,R$ satisfying finitely many equational laws. Examples include DRC-semigroups (hence Ehresmann semigroups), which also satisfy the congruence conditions. The ample conditions on DR-semigroups are studied here and are defined by the laws $$xD(y)=D(xD(y))x\mbox{ and }R(y)x=xR(R(y)x).$$ Two natural partial orders may be defined on a DR-semigroup and we show that the ample conditions hold if and only if the two orders are equal and the projections (elements of the form $D(x)$) commute with one-another. Restriction semigroups satisfy the generalized ample conditions, but we give other examples using strongly order-preserving functions on a quasiordered set as well as so-called ``double demonic" composition on binary relations. Following the work of Stein, we show how to construct a certain partial algebra $C(S)$ from any DR-semigroup, which is a category if $S$ satisfies the congruence conditions, but is ``almost" a category if the ample conditions hold. We then characterise the ample conditions in terms of a converse of the condition on $S$ ensuring that $C(S)$ is a category. Our main result is an ESN-style theorem for DR-semigroups satisfying the ample conditions, based on the $C(S)$ construction. We also obtain an embedding theorem, generalizing a result for restriction semigroups due to Lawson.

Type families on higher inductive types such as pushouts can capture homotopical properties of differential geometric constructions including connections, curvature, and vector fields. We define a class of pushouts based on simplicial complexes, then define principal bundles, connections, and curvature on these. We provide an example of a tangent bundle but do not prove when these must exist. We define vector fields, and the index of a vector field. Our main result is a theorem relating total curvature and total index, a key step to proving the Gauss-Bonnet theorem and the Poincar\'e-Hopf theorem, but without an existing definition of Euler characteristic to compare them to. We draw inspiration in part from the young field of discrete differential geometry, and in part from the original classical proofs, which often make use of triangulations and other discrete arguments.

Johnstone demonstrated that Heyting semilattices form a semi-abelian category via a specific triple of terms. Inspired by this work, we introduce \emph{Johnstone algebras} or J-algebras. The algebraic $(*,\to,e)$-theory $J$ of arities $(2,2,0)$ consists of three axioms carefully chosen to ensure protomodularity in alignment with Johnstone's terms. Johnstone algebras generalize well-known structures such as groups (division) and Heyting semilattices (implication) providing a unified framework within the well-behaved setting of semi-abelian categories. We present two primary contributions. First, we identify the M-axiom, \[ (t(x,y)\to x)\to (t(x,y)\to z) \approx x\to z, \text{ where }t(x,y) = (x\to y)\to y. \] The M-axiom is satisfied by residuated Johnstone algebras, and it can be considered a weakening of the H-axiom to comparable elements. We show that $t(x,y)$ defines a \emph{relative closure term} in MBC-algebras, and it implies that MBC-algebras form a variety of algebras, thereby generalizing the corresponding theorem related to HBCK-algebras. Second, we prove several no-go results, demonstrating that balanced theories or theories admitting non-discrete monotone or inflationary algebras cannot possess Malcev terms. Together, these results establish Johnstone algebras as significant structures that achieve desirable categorical properties by carefully integrating both logical and symmetric features, while closely avoiding the constraints imposed by our no-go results.

This paper introduces an inherently strict presentation of categories with products, coproducts, or symmetric monoidal products that is inspired by file systems and directories. Rather than using nested binary tuples to combine objects or morphisms, the presentation uses named tuples. Specifically, we develop 2-monads whose strict 2-algebras are product categories, coproduct categories, or symmetric monoidal categories, in a similar vein to the classical Fam construction, but where the elements of the indexing set are period-separated identifiers like $\mathtt{cart.motor.momentum}$. Our development of directories is also intended to serve the secondary purpose of expositing certain aspects of polynomial monads, and is accompanied by Haskell code that shows how the mathematical ideas can be implemented.

We construct a triangulated equivalence between the derived categories of quasi-coherent and contraherent $\mathcal A$-modules for a quasi-coherent quasi-algebra $\mathcal A$ over a quasi-compact semi-separated scheme $X$. The sheaf of rings of differential operators $\mathcal D$ (or fiberwise differential operators for a smooth morphism of schemes) is the thematic example of a quasi-coherent quasi-algebra.

We investigate how to add a symmetric monoidal structure to quantaloids in a compatible way. In particular, dagger compact quantaloids turn out to have properties that are similar to the category Rel of sets and binary relations. Examples of such quantaloids are the category qRel of quantum sets and binary relations, and the category V-Rel of sets and binary relations with values in a commutative unital quantale V. For both examples, the process of internalization structures is of interest. Discrete quantization, a process of generalization mathematical structures to the noncommutative setting can be regarded as the process of internalizing these structures in qRel, whereas fuzzification, the process of introducing degrees of truth or membership to concepts that are traditionally considered either true or false, can be regarded as the process of internalizing structures in V-Rel. Hence, we investigate how to internalize power sets and preordered structures in dagger compact quantaloids.

Let $G$ be a finite group. In this paper, we first introduce a new notion, so-called the Mackey double category of $G$. Then we prove that the category of Mackey double categories and the category of Mackey functors of $G$ are equivalent.

It was conjectured at the end of the book "Representation theory of Artin algebras" by M. Auslander, I. Reiten and S. Smalo that an Artin algebra with the property that its finitely generated indecomposable modules are up to isomorphism completely determined by theirs composition factors is of finite representation type. Examples of rings with this property are the semisimple artinian rings and the rings of the form $\mathbb{Z}_n$. An affirmative answer is obtained for some special cases, namely, the commutative, the hereditary and the radical square zero case.

The orbifold/condensation completion procedure of defect topological quantum field theories can be seen as carrying out a lattice or state sum model construction internal to an ambient theory. In this paper, we propose a conceptual algebraic description of orbifolds/condensations for arbitrary tangential structures in terms of higher dagger structures and higher idempotents. In particular, we obtain (oriented) orbifold completion from (framed) condensation completion by using a general strictification procedure for higher dagger structures which we describe explicitly in low dimensions; we also discuss the spin and unoriented case. We provide several examples of higher dagger categories, such as those associated to state sum models, (orbifolds of) Landau--Ginzburg models, and truncated affine Rozansky--Witten models. We also explain how their higher dagger structures are naturally induced from rigid symmetric monoidal structures, recontextualizing and extending results from the literature.

Our research builds upon Halmos's foundational work on functional monadic Boolean algebras and our previous work on tense operators to develop three essential constructions, including the important concepts of fuzzy sets and powerset operators. These constructions have widespread applications across contemporary mathematical disciplines, including algebra, logic, and topology. The framework we present generates four covariant and two contravariant functors, establishing three adjoint situations.

We use Kan injectivity to axiomatise concepts in the 2-category of topoi. We showcase the expressivity of this language through many examples, and we establish some aspects of the formal theory of Kan extension in this 2-category (pointwise Kan extensions, fully faithful morphisms, etc.). We use this technology to introduce fragments of geometric logic, and we accommodate essentially algebraic, disjunctive, regular, and coherent logic in our framework, together with some more exotic examples. We show that each fragment $\mathcal{H}$ in our sense identifies a lax-idempotent (relative) pseudomonad $\mathsf{T}^{\mathcal{H}}$ on $\mathsf{lex}$, the $2$-category of finitely complete categories. We show that the algebras for $\mathsf{T}^{\mathcal{H}}$ admit a notion of classifying topos, for which we deliver several Diaconescu-type results. The construction of classifying topoi allows us to define conceptually complete fragments of geometric logic.

We determine the Balmer spectrum of dualisable objects in the stable module category for $\mathrm{H}_1\mathfrak{F}$ groups of type $\mathrm{FP}_{\infty}$ and show that the telescope conjecture holds for these categories. We also determine the spectrum of dualisable objects for certain infinite free products of finite groups. Using this, we give examples where the stable category is not stratified by the spectrum of dualisable objects and where the telescope conjecture does not hold.

For an $(\infty,n)$-category $\mathscr E$ we define an $(\infty,1)$ category $\mathrm{TwAr}(\mathscr E)$ and provide an isomorphism between the stabilization of the overcategory of $\mathscr E$ in $\mathrm{Cat}_{(\infty,n)}$ and the $\infty$-category of spectrum-valued functors on $\mathrm{TwAr}(\mathscr E)$. We use this to develop the deformation theory of $(\infty,n)$-categories and apply it to given an $\infty$-categorical characterization of lax-idempotent monads.