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We treat spectral problems by twisted groupoid methods. To Hausdorff locally compact groupoids endowed with a continuous $2$-cocycle one associates the reduced twisted groupoid $C^*$-algebra. Elements (or multipliers) of this algebra admit…

Operator Algebras · Mathematics 2020-07-07 M. Mantoiu

The concept of homotopic distance and its higher analog are introduced in [6]. In this paper we introduce some important properties of higher homotopic distance, investigate the conditions under which $\cat$, $\secat$ and higher dimensional…

Algebraic Topology · Mathematics 2019-07-22 Ayse Borat , Tane Vergili

In these notes we give a brief introduction to decomposition theory and we summarize some classical and well-known results. The main question is that if a partitioning of a topological space (in other words a decomposition) is given, then…

Geometric Topology · Mathematics 2021-03-05 Boldizsar Kalmar

We provide a ZFC example of a compact space K such that C(K)* is w*-separable but its closed unit ball is not w*-separable. All previous examples of such kind had been constructed under CH. We also discuss the measurability of the supremum…

Functional Analysis · Mathematics 2014-06-30 Antonio Avilés , Grzegorz Plebanek , José Rodríguez

This paper is concerned with the axiomatic basis of structures within Hypercompositional Algebra. It is proven that the axioms employed in the definition of numerous hypercompositional structures lack independence. Accordingly, novel…

Rings and Algebras · Mathematics 2026-03-05 Christos G. Massouros

Finite topological spaces became much more essential in topology, with the development of computer science. The task of this paper is to study and investigate some properties of such spaces with the existence of an ordered relation between…

General Topology · Mathematics 2007-05-23 A. El-Fattah El-Atik , M. E. Abd El-Monsef , E. I. Lashin

The notion of bounded element of C*-inductive locally convex spaces (or C*-inductive partial *-algebras) is introduced and discussed in two ways: the first one takes into account the inductive structure provided by certain families of…

Operator Algebras · Mathematics 2013-07-29 Giorgia Bellomonte , Salvatore Di Bella , Camillo Trapani

Using the natural duality between linear functionals on tensor products of C*-algebras with the trace class operators on a Hilbert space H and linear maps of the C*-algebra into B(H), we give two characterizations of separability, one…

Operator Algebras · Mathematics 2008-04-01 Erling Stormer

We prove a sandwiching lemma for inner-exact locally compact Hausdorff \'etale groupoids. Our lemma says that every ideal of the reduced $C^*$-algebra of such a groupoid is sandwiched between the ideals associated to two uniquely defined…

Operator Algebras · Mathematics 2024-02-28 Kevin Aguyar Brix , Toke Meier Carlsen , Aidan Sims

We study the range of a classifiable class ${\cal A}$ of unital separable simple amenable $C^*$-algebras which satisfy the Universal Coefficient Theorem. The class ${\cal A}$ contains all unital simple AH-algebras. We show that all unital…

Operator Algebras · Mathematics 2008-08-27 Huaxin Lin , Zhuang Niu

We prove a category-theoretic independence theorem for four fundamental notions: meaning, object, name, and existence. Working in a Lawvere-style categorical semantics and in particular in toposes, we show that these notions occupy distinct…

Category Theory · Mathematics 2026-02-23 Takao Inoué

In \cite{To} S. Todorcevic introduced the notion of a topological Ramsey space and a list of axioms required to be satisfied by any such a space. Here we show that any topological Ramsey space that satisfies a strengthened version of one of…

Logic · Mathematics 2017-03-20 Dimitris Vlitas

Motivated by algebraic quantum field theory and our previous work we study properties of inductive systems of \ $C^*$-algebras over arbitrary partially ordered sets. A partially ordered set can be represented as the union of the family of…

Operator Algebras · Mathematics 2019-03-27 Renat Gumerov , Ekaterina Lipacheva , Tamara Grigoryan

In this paper we introduce primigraph spaces, which are topological spaces together with a sheaf of $C^*$-algebras that can be covered by some Prim A's, that is, by the primitive spectra of some $C^*$-algebras endowed with Jacobson topology…

Operator Algebras · Mathematics 2020-05-18 Manuel Norman

Inspired by the classical category theorems of Halmos and Rohlin for the discrete measure preserving transformations, we prove analogous results in the abstract setting of unitary and isometric C_0-semigroups on a separable Hilbert space.…

Functional Analysis · Mathematics 2010-08-18 Tanja Eisner , Andras Sereny

We give new characterizations of spaces $X$ which are $k_\mathbb{R}$-spaces or $s_\mathbb{R}$-spaces. Applying the obtained results we provide some sufficient and necessary conditions on $X$ for which $C_p(X)$ is a $k_\mathbb{R}$-space or…

General Topology · Mathematics 2025-06-19 Saak Gabriyelyan , Evgenii Reznichenko

We introduce classical properties using the concept of super selection rule, i.e. two properties are separated by a superselection rule iff there do not exist 'superposition states' related to these two properties. Then we show that the…

Quantum Physics · Physics 2010-04-16 Diederik Aerts , Didier Deses

We introduce cs-topologies, or topologies of open complemented subsets, as a new approach to constructive topology that preserves the duality between open and closed subsets of classical topology. Complemented subsets were used successfully…

General Topology · Mathematics 2025-01-30 Iosif Petrakis

In this work, new equivalences of topological statements and weaker axioms than ${\bf AC}$ are proven. This equivalences include the use of anti-properties. All this equivalences have been checked with a computer using the theorem proving…

General Topology · Mathematics 2015-11-02 Daniel de-la-Concepción

We introduce the notion of the separated pair of closed submodules in the setting of Hilbert $C^*$-modules. We demonstrate that even in the case of Hilbert spaces this concept has several nice characterizations enriching the theory of…

Operator Algebras · Mathematics 2024-05-09 R. Eskandari , W. Luo , M. S. Moslehian , Q. Xu , H. Zhang