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Let $R$ be any ring with identity. We show that the homotopy category of all acyclic chain complexes of pure-projective $R$-modules is a compactly generated triangulated category. We do this by constructing abelian model structures that put…

Algebraic Topology · Mathematics 2022-01-21 James Gillespie

We define a new notion of an algebraic model structure, in which the cofibrations and fibrations are retracts of coalgebras for comonads and algebras for monads, and prove "algebraic" analogs of classical results. Using a modified version…

Category Theory · Mathematics 2011-03-14 Emily Riehl

Extensivity of a category may be described as a property of coproducts in the category, namely, that they are disjoint and universal. An alternative viewpoint is that it is a property of morphisms in a category. This paper explores this…

Category Theory · Mathematics 2025-02-19 Michael Hoefnagel , Emma Theart

We give a model-independent construction of directed univalent cocartesian fibrations of $(\infty,1)$-categories, and prove a straightening equivalence against such fibrations. The key step is showing that cocartesian fibrations descend…

Category Theory · Mathematics 2026-03-31 Christian Sattler , David Wärn

The homotopy category of a model structure on a weakly idempotent complete additive category is proved to be equivalent to the additive quotient of the category of cofibrant-fibrant objects with respect to the subcategory of…

Representation Theory · Mathematics 2025-01-28 Xue-Song Lu , Pu Zhang

A model category is called combinatorial if it is cofibrantly generated and its underlying category is locally presentable. As shown in recent years, homotopy categories of combinatorial model categories share useful properties, such as…

Algebraic Topology · Mathematics 2020-12-04 Carles Casacuberta , Jiri Rosicky

The functor that takes a ring to its category of modules has an adjoint if one remembers the forgetful functor to abelian groups: the endomorphism ring of linear natural transformations. This uses the self-enrichment of the category of…

Category Theory · Mathematics 2020-03-09 Gabriel C. Drummond-Cole , Joseph Hirsh , Damien Lejay

We consider branched coverings which are simple in the sense that any point of the target has at most one singular preimage. The cobordism classes of $k$-fold simple branched coverings between $n$-manifolds form an abelian group…

Geometric Topology · Mathematics 2017-07-11 Csaba Nagy

We provide conditions on a monoidal model category $\mathcal{M}$ so that the category of commutative monoids in $\mathcal{M}$ inherits a model structure from $\mathcal{M}$ in which a map is a weak equivalence or fibration if and only if it…

Algebraic Topology · Mathematics 2021-09-14 David White

We give a construction that identifies the collection of pure processes (i.e. those which are deterministic, or without randomness) within a theory containing both pure and mixed processes. Working in the framework of symmetric monoidal…

Quantum Physics · Physics 2018-03-05 Oscar Cunningham , Chris Heunen

Using a categorial version of Fra\"iss\'e's theorem due to Droste and G\"obel, we derive a criterion for a comma-category to have universal homogeneous objects. As a first application we give new existence result for universal structures…

Category Theory · Mathematics 2013-02-26 Christian Pech , Maja Pech

Cofibrations are defined in the category of Fr\"olicher spaces by weakening the analog of the classical definition to enable smooth homotopy extensions to be more easily constructed, using flattened unit intervals. We later relate smooth…

Algebraic Topology · Mathematics 2019-08-19 B. Dugmore , PP. Ntumba

In this note we prove that every finite collection of connected algebraic subgroups of the group of triangular automorphisms of the affine space generates a connected solvable algebraic subgroup.

Algebraic Geometry · Mathematics 2022-03-15 Ivan Arzhantsev , Kirill Shakhmatov

Given a compact, oriented, connected surface $F$, we show that the set of connected sutured manifolds $(M,\gamma)$ with $R_{\pm}(\gamma)\cong F$ is generated by the product sutured manifold $(F,\partial F)\times[0,1]$ through surgery…

Geometric Topology · Mathematics 2025-02-06 Yi Ni

A non-unital algebra in a closed monoidal category is called self-induced if the multiplication induces an isomorphism between A\otimes_A A and A. For such an algebra, we define smoothening and roughening functors that retract the category…

Rings and Algebras · Mathematics 2015-10-23 Ralf Meyer

We introduce a monoidal category whose morphisms are finite partial orders, with chosen minimal and maximal elements as source and target respectively. After recalling the notion of presentation of a monoidal category by the means of…

Logic in Computer Science · Computer Science 2015-05-28 Samuel Mimram

We show that the homotopy category of complexes K(B) over any finitely accessible additive category B is locally well generated. That is, any localizing subcategory L in K(B) which is generated by a set is well generated in the sense of…

Category Theory · Mathematics 2010-06-23 Jan Stovicek

We present a family of model structures on the category of multicomplexes. There is a cofibrantly generated model structure in which the weak equivalences are the morphisms inducing an isomorphism at a fixed stage of an associated spectral…

Algebraic Topology · Mathematics 2021-01-13 Xin Fu , Ai Guan , Muriel Livernet , Sarah Whitehouse

We furnish any category of a universal (co)homology theory. Universal (co)homologies and universal relative (co)homologies are obtained by showing representability of certain functors and take values in $R$-linear abelian categories of…

Algebraic Geometry · Mathematics 2023-05-10 L. Barbieri-Viale

Necessary and sufficient conditions are given for the endomorphism monoid of a profinite semigroup to be profinite. A similar result is established for the automorphism group.

Group Theory · Mathematics 2010-03-22 Benjamin Steinberg