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We introduce the notions of triviality and order-triviality for global invariant types in an arbitrary first-order theory and show that they are well behaved in the NIP context. We show that these two notions agree for invariant global…

Logic · Mathematics 2026-02-24 Slavko Moconja , Predrag Tanović

In this work we discuss a new type of factorisation systems for \textbf{Ord}-enriched categories. We start by defining the new notion of lax weak orthogonality, which involves the existence of lax diagonal morphisms for lax squares. Using…

Category Theory · Mathematics 2021-03-16 Leonardo Larizza

Let G be a compact connected Lie group. We prove that the Fourier algebra A(G) is weakly amenable if and only if G is abelian.

Functional Analysis · Mathematics 2007-05-23 R. J. Plymen

We study the structure of the category of representations of $\mathbf{FA}$, the category of finite sets and all maps, mostly working over a field of characteristic zero. This category is not semi-simple and exhibits interesting features. We…

Representation Theory · Mathematics 2025-09-16 Geoffrey Powell

There is a well-known correspondence between coherent theories (and their interpretations) and coherent categories (resp. functors), hence the (2,1)-category $\mathbf{Coh_{\sim}}$ (of small coherent categories, coherent functors and all…

Category Theory · Mathematics 2021-04-28 Kristóf Kanalas

Let $\kappa$ be a regular cardinal, $\lambda<\kappa$ be a smaller infinite cardinal, and $\mathsf K$ be a $\kappa$-accessible category where colimits of $\lambda$-indexed chains exist. We show that various category-theoretic constructions…

Category Theory · Mathematics 2024-10-16 Leonid Positselski

In this paper we present a new way to construct the pro-category of a category. This new model is very convenient to work with in certain situations. We present a few applications of this new model, the most important of which solves an…

Category Theory · Mathematics 2014-06-25 Ilan Barnea , Tomer M. Schlank

We present an efficient and user-friendly method for constructing any cofibrantly generated model structure on the category of double categories whose trivial fibrations are the "canonical" ones: the double functors which are surjective on…

Algebraic Topology · Mathematics 2025-09-30 Lyne Moser , Maru Sarazola , Paula Verdugo

We prove existence results for small presentations of model categories generalizing a theorem of D. Dugger from combinatorial model categories to more general model categories. Some of these results are shown under the assumption of…

Algebraic Topology · Mathematics 2017-10-17 G. Raptis , J. Rosický

We extend Goodwillie's classification of finitary linear functors to arbitrary small functors. That is we show that every small linear simplicial functor from spectra to simplicial sets is weakly equivalent to a filtered colimit of…

Algebraic Topology · Mathematics 2015-10-20 Boris Chorny

In this note we show that a semisimplicial set with the weak Kan condition admits a simplicial structure, provided any object allows an idempotent self-equivalence. Moreover, any two choices of simplicial structures give rise to equivalent…

Algebraic Topology · Mathematics 2018-02-27 Wolfgang Steimle

The two model-theoretic concepts of weak saturation and weak amalgamation property are studied in the context of accessible categories. We relate these two concepts providing sufficient conditions for existence and uniqueness of weakly…

Category Theory · Mathematics 2025-08-06 Ivan Di Liberti

We define the notion of accessibility for a pro-$p$ group. We prove that finitely generated pro-$p$ groups are accessible given a bound on the size of their finite subgroups. We then construct a finitely generated inaccessible pro-$p$…

Group Theory · Mathematics 2018-11-07 Gareth Wilkes

In this paper, we establish a theorem that proves a condition when an inclusion morphism between simplicial sets becomes a weak homotopy equivalence. Additionally, we present two applications of this result. The first application…

Algebraic Topology · Mathematics 2024-05-07 Hisato Matsukawa

We consider the problem of approximating an affinely structured matrix, for example a Hankel matrix, by a low-rank matrix with the same structure. This problem occurs in system identification, signal processing and computer algebra, among…

Numerical Analysis · Mathematics 2014-06-25 Mariya Ishteva , Konstantin Usevich , Ivan Markovsky

This thesis is devoted to the proof of a theorem showing the existence of a closed model category structure for weakly enriched categories. It requires first of all the definitions of weakly enriched categories and equivalences of weakly…

Algebraic Topology · Mathematics 2007-05-23 Regis Pellissier

The concept of a weak factorization system has been studied extensively in homotopy theory and has recently found an application in one of the proofs of the celebrated flat cover conjecture, categorical versions of which have been presented…

Group Theory · Mathematics 2013-02-04 Alex Bailey , James Renshaw

We introduce a new class of higher categorical structures called weakly globular Tamsamani n-categories. These generalize the Tamsamani-Simpson model of higher categories by using the new paradigm of weak globularity to weaken higher…

Category Theory · Mathematics 2016-09-15 Simona Paoli

Variations on the notions of Reedy model structures and projective model structures on categories of diagrams in a model category are introduced. These allow one to choose only a subset of the entries when defining weak equivalences, or to…

Algebraic Topology · Mathematics 2010-04-23 Mark W. Johnson

We show that every combinatorial model category can be obtained, up to Quillen equivalence, by localizing a model category of diagrams of simplicial sets. This says that any combinatorial model category can be built up from a category of…

Algebraic Topology · Mathematics 2007-05-23 Daniel Dugger