{"title":"Winding number of loops and digital category of digital simple closed curves","authors":"Samia Ashraf, Amna Amanat Ali","doi":"10.1016/j.topol.2025.109410","DOIUrl":"10.1016/j.topol.2025.109410","url":null,"abstract":"<div><div>An analogue of the notion of Lusternik–Schnirelmann category for digital images, named “digital category” is defined to be one less than the number of “subdivision categorical” sets which cover the digital image. We define winding number of loops in digital simple closed 8-curves and use it to compute their digital category. Moreover, by applying this to a specific family of digital simple closed curves, we deduce that the digital category of <span><math><mi>S</mi><mo>(</mo><mi>D</mi><mo>,</mo><mi>n</mi><mo>)</mo></math></span>, the <em>n</em>-subdivision of the smallest such curve <em>D</em> consisting of four points (digital circle of radius 1) is equal to the digital category of <em>D</em> itself.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"370 ","pages":"Article 109410"},"PeriodicalIF":0.6,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143936490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Combinatorially rich sets in partial semigroups","authors":"Arpita Ghosh , Neil Hindman","doi":"10.1016/j.topol.2025.109406","DOIUrl":"10.1016/j.topol.2025.109406","url":null,"abstract":"<div><div>There are several notions of size for semigroups that have natural analogues for partial semigroups. Among these are <em>thick</em>, <em>syndetic</em>, <em>central</em>, <em>piecewise syndetic</em>, <em>IP</em>, <em>J</em>, and the more recently introduced notion of <em>combinatorially rich</em>, abbreviated CR. We investigate the notion of CR set for adequate partial semigroups, its relation to other notions, especially J sets, and some surprising differences among them.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109406"},"PeriodicalIF":0.6,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143922306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Observations on a cardinality bound involving the weak Lindelöf degree","authors":"Désirée Basile , Angelo Bella , Nathan Carlson","doi":"10.1016/j.topol.2025.109405","DOIUrl":"10.1016/j.topol.2025.109405","url":null,"abstract":"<div><div>We present partial answers to two questions related to cardinality bounds involving the weak Lindelöf degree. The main tools will be a cardinal invariant which is a sort of “measure of quasi-regularity” and a variation on the classical notion of tightness.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109405"},"PeriodicalIF":0.6,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143886360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The Δ1-property of X is equivalent to the Choquet property of B1(X)","authors":"Alexander V. Osipov","doi":"10.1016/j.topol.2025.109395","DOIUrl":"10.1016/j.topol.2025.109395","url":null,"abstract":"<div><div>We give a characterization of the <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-property of any Tychonoff space <em>X</em> in terms of the function space <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span> of all Baire-one real-valued functions on a space <em>X</em> with the topology of pointwise convergence. We establish that for a Tychonoff space <em>X</em> the <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-property is equivalent to the Choquet property of <span><math><msub><mrow><mi>B</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span>. Also we construct under <em>ZFC</em> an example of a separable pseudocompact space <em>X</em> such that <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span> is <em>κ</em>-Fréchet-Urysohn but <em>X</em> fails to be a <span><math><msub><mrow><mi>Δ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-space. This answers a question of Ka̧kol-Leiderman-Tkachuk.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"370 ","pages":"Article 109395"},"PeriodicalIF":0.6,"publicationDate":"2025-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143903974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Topological properties determined by closures of countable sets","authors":"V.V. Tkachuk","doi":"10.1016/j.topol.2025.109393","DOIUrl":"10.1016/j.topol.2025.109393","url":null,"abstract":"<div><div>We establish that a locally convex space must be metrizable if it has a Čech-complete dense subspace and show that there are locally convex spaces <em>L</em> of arbitrarily large extent such that <span><math><mover><mrow><mi>A</mi></mrow><mo>‾</mo></mover></math></span> is <em>σ</em>-compact for any countable set <span><math><mi>A</mi><mo>⊂</mo><mi>L</mi></math></span>. Under Jensen's Axiom (⋄), we give an example of a metrizable space <em>M</em> which does not have a dense Čech-complete subspace while <span><math><mover><mrow><mi>A</mi></mrow><mo>‾</mo></mover></math></span> is Čech-complete for every countable set <span><math><mi>A</mi><mo>⊂</mo><mi>M</mi></math></span>. Our results give a consistent answer to two published open questions.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109393"},"PeriodicalIF":0.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143859153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Cohomology bases of toric surfaces","authors":"Xin Fu , Tseleung So , Jongbaek Song","doi":"10.1016/j.topol.2025.109392","DOIUrl":"10.1016/j.topol.2025.109392","url":null,"abstract":"<div><div>Given a compact toric surface, the multiplication of its rational cohomology can be described in terms of the intersection products of Weil divisors, or in terms of the cup products of cohomology classes representing specific cells. In this paper, we aim to compare these two descriptions. More precisely, we define two different cohomology bases, the <em>Poincaré dual basis</em> and the <em>cellular basis</em>, which give rise to matrices representing the intersection product and the cup product. We prove that these representing matrices are inverse of each other.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109392"},"PeriodicalIF":0.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143863528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On isometric universality of spaces of metrics","authors":"Yoshito Ishiki , Katsuhisa Koshino","doi":"10.1016/j.topol.2025.109394","DOIUrl":"10.1016/j.topol.2025.109394","url":null,"abstract":"<div><div>A metric space <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>d</mi><mo>)</mo></math></span> is said to be universal for a class of metric spaces if all metric spaces in the class can be isometrically embedded into <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>d</mi><mo>)</mo></math></span>. In this paper, for a metrizable space <em>Z</em> possessing abundant subspaces, we first investigate the universality of the space of metrics on <em>Z</em>. Next, in contrast, we show that if <em>Z</em> is an infinite discrete space, then the space of metrics on <em>Z</em> is universal for all metric spaces having the same weight of <em>Z</em>. As a corollary of our results, if <em>Z</em> is non-compact, or uncountable and compact, then the space of metrics on <em>Z</em> is universal for all compact metric spaces. In addition, if <em>Z</em> is compact and countable, then there exists a compact metric space that can not be isometrically embedded into the space of metrics on <em>Z</em>.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109394"},"PeriodicalIF":0.6,"publicationDate":"2025-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143863527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Bar-Natan theory and tunneling between incompressible surfaces in 3-manifolds","authors":"Uwe Kaiser","doi":"10.1016/j.topol.2025.109390","DOIUrl":"10.1016/j.topol.2025.109390","url":null,"abstract":"<div><div>In <span><span>[16]</span></span> the author defined for each commutative Frobenius algebra a skein module of surfaces in a 3-manifold <em>M</em> bounding a closed 1-manifold <span><math><mi>α</mi><mo>⊂</mo><mo>∂</mo><mi>M</mi></math></span>. The surface components are colored by elements of the Frobenius algebra. The modules are called the Bar-Natan modules of <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>α</mi><mo>)</mo></math></span>. In this article we show that Bar-Natan modules are colimit modules of functors associated to Frobenius algebras, <em>decoupling</em> topology from algebra. The functors are defined on a category of 3-dimensional compression bordisms embedded in cylinders over <em>M</em> and take values in a linear category defined from the Frobenius algebra. The relation with the <span><math><mn>1</mn><mo>+</mo><mn>1</mn></math></span>-dimensional topological quantum field theory functor associated to the Frobenius algebra is studied. We show that the geometric content of the skein modules is contained in a <em>tunneling graph</em> of <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>α</mi><mo>)</mo></math></span>, providing a natural presentation of the Bar-Natan module by application of the functor defined from the algebra. Such presentations have essentially been stated in <span><span>[16]</span></span> and <span><span>[2]</span></span> using ad-hoc arguments. But they appear naturally on the background of the Bar-Natan functor and associated categorical considerations. We discuss in general how to deduce presentations of colimit modules for functors into module categories in terms of minimal terminal sets of objects of the category in the categorical setting. We also sketch the construction of a bicategory version of the Bar-Natan functor.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109390"},"PeriodicalIF":0.6,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143863529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An answer to a problem on topologies of function spaces on metric measure spaces","authors":"Hanbiao Yang , Kaihong Dong , Yingying Jin","doi":"10.1016/j.topol.2025.109391","DOIUrl":"10.1016/j.topol.2025.109391","url":null,"abstract":"<div><div>Let <em>X</em> be a metric measure space. In the paper K. Koshino (2020) <span><span>[6]</span></span>, it was proved that if <em>X</em> satisfies some conditions, then the <span><math><msup><mrow><mi>L</mi></mrow><mrow><mi>p</mi></mrow></msup></math></span>-space <span><math><msup><mrow><mi>L</mi></mrow><mrow><mi>p</mi></mrow></msup><mo>(</mo><mi>X</mi><mo>)</mo></math></span> on <em>X</em> is homeomorphic to the product space <em>s</em> of countably infinitely many open intervals <span><math><mo>(</mo><mo>−</mo><mn>1</mn><mo>,</mo><mn>1</mn><mo>)</mo></math></span>, and the subspace <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>u</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span> of <span><math><msup><mrow><mi>L</mi></mrow><mrow><mi>p</mi></mrow></msup><mo>(</mo><mi>X</mi><mo>)</mo></math></span> consisting of uniformly continuous maps is also homeomorphic to the subspace <span><math><msub><mrow><mi>c</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> of <em>s</em> consisting of sequences converging to 0. Then it was asked whether or not the pair <span><math><mo>(</mo><msup><mrow><mi>L</mi></mrow><mrow><mi>p</mi></mrow></msup><mo>(</mo><mi>X</mi><mo>)</mo><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>u</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><mo>)</mo></math></span> is homeomorphic to <span><math><mo>(</mo><mi>s</mi><mo>,</mo><msub><mrow><mi>c</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>)</mo></math></span>. In this note, we will present some examples of metric measure spaces <em>X</em> in the both cases where those pairs are homeomorphic and not, and show that they are not homeomorphic if <em>X</em> is a Euclidean space or its cube with the usual metric and the Lebesgue measure.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"370 ","pages":"Article 109391"},"PeriodicalIF":0.6,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143903973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Enrique Castañeda-Alvarado, David Maya, Miguel Angel Morales-Bautista, Fernando Orozco-Zitli
{"title":"Induced mappings on Pixley-Roy hyperspace","authors":"Enrique Castañeda-Alvarado, David Maya, Miguel Angel Morales-Bautista, Fernando Orozco-Zitli","doi":"10.1016/j.topol.2025.109389","DOIUrl":"10.1016/j.topol.2025.109389","url":null,"abstract":"<div><div>The symbol <span><math><mrow><mi>PR</mi></mrow><mo>[</mo><mi>X</mi><mo>]</mo></math></span> denotes the hyperspace consisting of all nonempty finite subsets of a <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> topological space <em>X</em> endowed with the Pixley-Roy topology. For an onto mapping between <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> spaces <span><math><mi>f</mi><mo>:</mo><mi>X</mi><mo>→</mo><mi>Y</mi></math></span>, define the induced mapping <span><math><mrow><mi>PR</mi></mrow><mo>(</mo><mi>f</mi><mo>)</mo><mo>:</mo><mrow><mi>PR</mi></mrow><mo>[</mo><mi>X</mi><mo>]</mo><mo>→</mo><mrow><mi>PR</mi></mrow><mo>[</mo><mi>Y</mi><mo>]</mo></math></span> by <span><math><mrow><mi>PR</mi></mrow><mo>(</mo><mi>f</mi><mo>)</mo><mo>(</mo><mi>A</mi><mo>)</mo><mo>=</mo><mo>{</mo><mi>f</mi><mo>(</mo><mi>a</mi><mo>)</mo><mo>:</mo><mi>a</mi><mo>∈</mo><mi>A</mi><mo>}</mo></math></span> (the image of <em>A</em> under <em>f</em>). In this paper, we study the relationship between the condition <em>f</em> belongs to a class of mappings between <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> spaces <span><math><mi>M</mi></math></span> and the condition <span><math><mrow><mi>PR</mi></mrow><mo>(</mo><mi>f</mi><mo>)</mo></math></span> belongs to <span><math><mi>M</mi></math></span>.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"369 ","pages":"Article 109389"},"PeriodicalIF":0.6,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143844203","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}