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In \cite{E_2018}, Ern\'e relaxed the concept of sobriety in order to extend the theory of sober spaces and locally hypercompact spaces to situations where directed joins were missing, and introduced three kinds of non-sober spaces: cut…

General Topology · Mathematics 2019-07-16 Xinpeng Wen , Xiaoquan Xu

We first introduce and study two new classes of subsets in $T_0$ spaces - Rudin sets and $\wdd$ sets lying between the class of all closures of directed subsets and that of irreducible closed subsets. Using such subsets, we define three new…

General Topology · Mathematics 2019-09-23 Xiaoquan Xu , Chong Shen , Xiaoyong Xi , Dongsheng Zhao

In this paper, we will focus on k-bounded sober spaces and show the existence of a T_0 space X not admitting any k-bounded sobrification. This strengthens a result of Zhao, Lu and Wang, who proved that the canonical k-bounded sobrification…

General Topology · Mathematics 2020-11-24 Jing Lu , Kaiyun Wang , Guohua Wu , Bin Zhao

We introduce and study a new class of $T_0$ spaces, called open well-filtered spaces. The main results we proved include (1) every well-filtered space is an open well-filtered space; (2) every core-compact open well-filtered space is sober.…

General Topology · Mathematics 2023-06-22 Chong Shen , Xiaoyong Xi , Xiaoquan Xu , Dongsheng Zhao

In this paper, we provide a uniform approach to $d$-spaces, sober spaces and well-filtered spaces, and develop a general framework for dealing with all these spaces. For a subset system H, the theory of H-sober spaces and super H-sober…

General Topology · Mathematics 2020-03-18 Xiaoquan Xu

We prove that any weakly non-collapsed RCD space is actually non-collapsed, up to a renormalization of the measure. This confirms a conjecture raised by De Philippis and the second named author in full generality. One of the auxiliary…

Differential Geometry · Mathematics 2022-10-11 Camillo Brena , Nicola Gigli , Shouhei Honda , Xingyu Zhu

We show that the locally strongly sober spaces are exactly the coherent sober spaces that are weakly Hausdorff in the sense of Keimel and Lawson. This allows us to describe their Stone duals explicitly. As another application, we show that…

General Topology · Mathematics 2022-11-24 Jean Goubault-Larrecq

We first introduce and study two new classes of subsets in $T_0$ spaces - $\omega$-Rudin sets and $\omega$-well-filtered determined sets lying between the class of all closures of countable directed subsets and that of irreducible closed…

General Topology · Mathematics 2019-12-02 Xiaoquan Xu , Chong Shen , Xiaoyong Xi , Dongsheng Zhaod

A class of topological spaces is projective (resp., $\omega$-projective) if and only if projective systems of spaces (resp., with a countable cofinal subset of indices) in the class are still in the class. A certain number of classes of…

General Topology · Mathematics 2024-07-08 Jean Goubault-Larrecq

Based on topological Rudin's Lemma, we investigate two new kinds of sets - Rudin sets and well-filtered determined sets in $T_0$ topological spaces. Using such sets, we formulate and prove some new characterizations for well-filtered spaces…

General Topology · Mathematics 2019-11-27 Xiaoquan Xu , Dongsheng Zhao

We study associate and double associate spaces of two-weighted Sobolev spaces of the first order on real half-line and we show that unlike the notion of duality the associativity is divided into two cases which we call "strong" and "weak"…

Functional Analysis · Mathematics 2022-06-09 V. D. Stepanov , E. P. Ushakova

We define a class of subsets of a topological space that coincides with the class of compact saturated subsets when the space is sober, and with enough good properties when the space is not sober. This class is introduced especially in view…

General Topology · Mathematics 2011-06-21 Paul Poncet

In non-Hausdorff topology, many spaces exhibit significant separation properties, such as sober spaces, well-filtered spaces and d-spaces. These properties serve to fundamentally classify T0 topological spaces. In this paper, we introduce…

General Topology · Mathematics 2026-01-19 Xiangrui Li , Qingguo Li

We propose a notion of cusp forms on semisimple symmetric spaces. We then study the real hyperbolic spaces in detail, and show that there exists both cuspidal and non-cuspidal discrete series. In particular, we show that all the spherical…

Representation Theory · Mathematics 2012-08-08 Nils Byrial Andersen , Mogens Flensted-Jensen , Henrik Schlichtkrull

The open well-filtered spaces were introduced by Shen, Xi, Xu and Zhao to answer the problem whether every core-compact well-filtered space is sober. In the current paper we explore further properties of open well-filtered spaces. One of…

General Topology · Mathematics 2025-02-25 Chong Shen , Xiaoyong Xi , Dongsheng Zhao

In order to introduce the notion of causality in noncommutative geometry it is necessary to extend Gelfand theory to the context of ordered spaces. In a previous work we have already given an algebraic caracterization of the set of…

Operator Algebras · Mathematics 2015-06-18 Fabien Besnard

In this paper, we highlight some open problems stated by Xu and Zhao. In particular, we focus on strong $d$-spaces and answer two open problems concerning strong $d$-spaces. One is about the product space of an arbitrary family of strong…

General Topology · Mathematics 2021-09-24 Mengjie Jin , Hualin Miao , Qingguo Li

Recently, J. D. Lawson encouraged the domain theory community to consider the scientific program of developing domain theory in the wider context of $T_0$ spaces instead of restricting to posets. In this paper, we respond to this calling by…

Logic in Computer Science · Computer Science 2016-07-06 Hadrian Andradi , Weng Kin Ho

This paper presents three new families of fractional Sobolev spaces and their accompanying theory in one-dimension. The new construction and theory are based on a newly developed notion of weak fractional derivatives, which are natural…

Functional Analysis · Mathematics 2020-07-21 Xiaobing Feng , Mitchell Sutton

A non-empty subset of a topological space is irreducible if whenever it is covered by the union of two closed sets, then already it is covered by one of them. Irreducible sets occur in proliferation: (1) every singleton set is irreducible,…

Logic in Computer Science · Computer Science 2016-10-04 Hadrian Andradi , Weng Kin Ho
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