Pub Date : 2025-10-28DOI: 10.1016/j.topol.2025.109649
Jiuzhi Gao, Ziyu Huang
Let be a dynamical system with X a perfect Polish space and G a countable group, and let denote the collection of all compact subsets of X. It is shown that if Q is a , hereditary subset of and is the coherent list on X associated with Q, then a group action version of Kuratowski-Mycielski theorem holds.
Meanwhile, we construct a non-trivial transitive system with G a countable abelian group, such that there exist some special invariant chaotic sets in X. Specifically, there exists a G-invariant, n--scrambled, uniformly chaotic set in .
{"title":"On the group action version of the Kuratowski-Mycielski theorem and invariant chaotic sets","authors":"Jiuzhi Gao, Ziyu Huang","doi":"10.1016/j.topol.2025.109649","DOIUrl":"10.1016/j.topol.2025.109649","url":null,"abstract":"<div><div>Let <span><math><mo>(</mo><mi>X</mi><mo>,</mo><mi>G</mi><mo>)</mo></math></span> be a dynamical system with <em>X</em> a perfect Polish space and <em>G</em> a countable group, and let <span><math><mi>K</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> denote the collection of all compact subsets of <em>X</em>. It is shown that if <em>Q</em> is a <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>δ</mi></mrow></msub></math></span>, hereditary subset of <span><math><mi>K</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> and <span><math><msub><mrow><mi>α</mi></mrow><mrow><mi>Q</mi></mrow></msub><mo>=</mo><msub><mrow><mo>{</mo><msubsup><mrow><mi>R</mi></mrow><mrow><mi>n</mi></mrow><mrow><mi>Q</mi></mrow></msubsup><mo>}</mo></mrow><mrow><mi>n</mi><mo>∈</mo><mi>N</mi></mrow></msub></math></span> is the coherent list on <em>X</em> associated with <em>Q</em>, then a group action version of Kuratowski-Mycielski theorem holds.</div><div>Meanwhile, we construct a non-trivial transitive system <span><math><mo>(</mo><mi>X</mi><mo>,</mo><mi>G</mi><mo>)</mo></math></span> with <em>G</em> a countable abelian group, such that there exist some special invariant chaotic sets in <em>X</em>. Specifically, there exists a <em>G</em>-invariant, <em>n</em>-<span><math><msub><mrow><mi>δ</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>-scrambled, uniformly chaotic set in <span><math><msub><mrow><mi>Σ</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109649"},"PeriodicalIF":0.5,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418012","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}
Pub Date : 2025-10-27DOI: 10.1016/j.topol.2025.109648
Yanhui Huang
In this paper, we discuss the relationships among -compactness, star countability, star Lindelöfness, star almost Lindelöfness and star weakly Lindelöfness in different spaces. We mainly give the following:
(1)
For a subspace X of an ordinal, X is star weakly Lindelöf if and only if it is -compact.
(2)
For subspaces A and B of an ordinal, is star weakly Lindelöf if and only if it is -compact.
(3)
For a subspace X of , X is star weakly Lindelöf if and only if it is -compact.
{"title":"Star covering properties of products of subspaces of ordinals","authors":"Yanhui Huang","doi":"10.1016/j.topol.2025.109648","DOIUrl":"10.1016/j.topol.2025.109648","url":null,"abstract":"<div><div>In this paper, we discuss the relationships among <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compactness, star countability, star Lindelöfness, star almost Lindelöfness and star weakly Lindelöfness in different spaces. We mainly give the following:<ul><li><span>(1)</span><span><div>For a subspace <em>X</em> of an ordinal, <em>X</em> is star weakly Lindelöf if and only if it is <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact.</div></span></li><li><span>(2)</span><span><div>For subspaces <em>A</em> and <em>B</em> of an ordinal, <span><math><mi>A</mi><mo>×</mo><mi>B</mi></math></span> is star weakly Lindelöf if and only if it is <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact.</div></span></li><li><span>(3)</span><span><div>For a subspace <em>X</em> of <span><math><msubsup><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></msubsup></math></span>, <em>X</em> is star weakly Lindelöf if and only if it is <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact.</div></span></li></ul></div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109648"},"PeriodicalIF":0.5,"publicationDate":"2025-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418008","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}
Pub Date : 2025-10-27DOI: 10.1016/j.topol.2025.109647
J.C. Ferrando , J. Ka̧kol
Let be the linear space of real-valued continuous functions with the pointwise topology. It is known that a Tychonoff space X is a Δ-space if and only if the locally convex space is distinguished. It has been recently shown that if there is a continuous linear surjection from onto and X is a Δ-space, Y is also a Δ-space. Here we investigate under what conditions the presence of a dense distinguished subspace E in leads X to be a Δ-space. We also produce a class of spaces for which contains a distinguished dense subspace.
{"title":"Distinguished dense Cp-subspaces","authors":"J.C. Ferrando , J. Ka̧kol","doi":"10.1016/j.topol.2025.109647","DOIUrl":"10.1016/j.topol.2025.109647","url":null,"abstract":"<div><div>Let <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow></math></span> be the linear space of real-valued continuous functions with the pointwise topology. It is known that a Tychonoff space <em>X</em> is a Δ-space if and only if the locally convex space <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span> is distinguished. It has been recently shown that if there is a continuous linear surjection from <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></math></span> onto <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>(</mo><mi>Y</mi><mo>)</mo></math></span> and <em>X</em> is a Δ-space, <em>Y</em> is also a Δ-space. Here we investigate under what conditions the presence of a dense distinguished subspace <em>E</em> in <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow></math></span> leads <em>X</em> to be a Δ-space. We also produce a class of spaces <span><math><mi>X</mi><mo>∉</mo><mi>Δ</mi></math></span> for which <span><math><msub><mrow><mi>C</mi></mrow><mrow><mi>p</mi></mrow></msub><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow></math></span> contains a distinguished dense subspace.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109647"},"PeriodicalIF":0.5,"publicationDate":"2025-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418009","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}
Pub Date : 2025-10-24DOI: 10.1016/j.topol.2025.109642
Colin Adams , Francisco Gomez-Paz , Jiachen Kang , Lukas Krause , Gregory Li , Chloe Marple , Ziwei Tan
Let be a compact and orientable 3-manifold. After capping off spherical boundaries with balls and removing any torus boundaries, we prove that the resulting manifold M contains handlebodies of arbitrary genus such that the closure of their complement is hyperbolic. We then extend the octahedral decomposition to obtain bounds on volume for some of these handlebody complements.
{"title":"Hyperbolic handlebody complements in 3-manifolds","authors":"Colin Adams , Francisco Gomez-Paz , Jiachen Kang , Lukas Krause , Gregory Li , Chloe Marple , Ziwei Tan","doi":"10.1016/j.topol.2025.109642","DOIUrl":"10.1016/j.topol.2025.109642","url":null,"abstract":"<div><div>Let <span><math><msub><mrow><mi>M</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> be a compact and orientable 3-manifold. After capping off spherical boundaries with balls and removing any torus boundaries, we prove that the resulting manifold <em>M</em> contains handlebodies of arbitrary genus such that the closure of their complement is hyperbolic. We then extend the octahedral decomposition to obtain bounds on volume for some of these handlebody complements.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109642"},"PeriodicalIF":0.5,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418007","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}
Pub Date : 2025-10-22DOI: 10.1016/j.topol.2025.109646
Valentin Keyantuo , Yevhen Zelenyuk
Let G be a countably infinite discrete group, let βG be the Stone-Čech compactification of G, and let . For every closed left ideal of βG, there is a finest decomposition of X into closed left ideals of βG with the property that the corresponding quotient space of X is Hausdorff. It is known that is nontrivial, and in fact , and for some , is nontrivial. We show that it is consistent with ZFC that, if G can be embedded algebraically into a compact group, then for every , is nontrivial.
{"title":"Closed left ideal decompositions of βG ∖ G and wandering points","authors":"Valentin Keyantuo , Yevhen Zelenyuk","doi":"10.1016/j.topol.2025.109646","DOIUrl":"10.1016/j.topol.2025.109646","url":null,"abstract":"<div><div>Let <em>G</em> be a countably infinite discrete group, let <em>βG</em> be the Stone-Čech compactification of <em>G</em>, and let <span><math><msup><mrow><mi>G</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>=</mo><mi>β</mi><mi>G</mi><mo>∖</mo><mi>G</mi></math></span>. For every closed left ideal <span><math><mi>X</mi><mo>⊆</mo><msup><mrow><mi>G</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math></span> of <em>βG</em>, there is a finest decomposition <span><math><mi>D</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> of <em>X</em> into closed left ideals of <em>βG</em> with the property that the corresponding quotient space of <em>X</em> is Hausdorff. It is known that <span><math><mi>D</mi><mo>(</mo><msup><mrow><mi>G</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>)</mo></math></span> is nontrivial, and in fact <span><math><mo>|</mo><mi>D</mi><mo>(</mo><msup><mrow><mi>G</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>)</mo><mo>|</mo><mo>=</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>c</mi></mrow></msup></math></span>, and for some <span><math><mi>X</mi><mo>∈</mo><mi>D</mi><mo>(</mo><msup><mrow><mi>G</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>)</mo></math></span>, <span><math><mi>D</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> is nontrivial. We show that it is consistent with ZFC that, if <em>G</em> can be embedded algebraically into a compact group, then for every <span><math><mi>X</mi><mo>∈</mo><mi>D</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, <span><math><mi>D</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> is nontrivial.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109646"},"PeriodicalIF":0.5,"publicationDate":"2025-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418006","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}
Pub Date : 2025-10-21DOI: 10.1016/j.topol.2025.109644
Qiling Liu
We prove that for an arbitrary g, there is a surface K of genus g embedded in , which has finitely many extendable self-homeomorphisms' action on , by defining a norm on and proving its additivity.
{"title":"Knotted surfaces, homological norm and extendable subgroup","authors":"Qiling Liu","doi":"10.1016/j.topol.2025.109644","DOIUrl":"10.1016/j.topol.2025.109644","url":null,"abstract":"<div><div>We prove that for an arbitrary <em>g</em>, there is a surface <em>K</em> of genus <em>g</em> embedded in <span><math><msup><mrow><mi>S</mi></mrow><mrow><mn>4</mn></mrow></msup></math></span>, which has finitely many extendable self-homeomorphisms' action on <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>(</mo><mi>K</mi><mo>,</mo><mi>Z</mi><mo>)</mo></math></span>, by defining a norm on <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>(</mo><mi>K</mi><mo>,</mo><mi>Z</mi><mo>)</mo></math></span> and proving its additivity.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109644"},"PeriodicalIF":0.5,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364655","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}
Pub Date : 2025-10-21DOI: 10.1016/j.topol.2025.109645
S. Kavitha , V. Renukadevi
Let be an involution on a manifold X with non empty fixed point set. The generalized Dold manifold is a space obtained as the quotient of by the action of defined by the fixed point free involution . When X is either a complex Grassmannian manifold or a complete flag manifold , we obtain the integral cohomology group of the generalized Dold manifolds and from the well known cell structures of complex Grassmannian and complete flag manifold. Also, we give the rational cohomology of the generalized Dold manifolds and .
设σ:X→X是流形X上具有非空不动点集的对合。广义Dold流形D(m,X)是由不动点自由对合(a, X)∑(- a,σ(X))定义的Z2作用下得到的作为Sm×X商的空间。当X是复格拉斯曼流形Gk(Cn)或完全标志流形F r (n)时,我们从已知的复格拉斯曼流形和完全标志流形的胞结构中得到广义Dold流形D(m,Gk(Cn))和D(m,F r (n))的积分上同调群。同时给出了广义Dold流形D(m,Gk(Cn))和D(m,F (n))的有理上同调。
{"title":"Integral and rational cohomologies of some generalized Dold manifolds","authors":"S. Kavitha , V. Renukadevi","doi":"10.1016/j.topol.2025.109645","DOIUrl":"10.1016/j.topol.2025.109645","url":null,"abstract":"<div><div>Let <span><math><mi>σ</mi><mo>:</mo><mi>X</mi><mo>→</mo><mi>X</mi></math></span> be an involution on a manifold <em>X</em> with non empty fixed point set. The generalized Dold manifold <span><math><mi>D</mi><mo>(</mo><mi>m</mi><mo>,</mo><mi>X</mi><mo>)</mo></math></span> is a space obtained as the quotient of <span><math><msup><mrow><mi>S</mi></mrow><mrow><mi>m</mi></mrow></msup><mo>×</mo><mi>X</mi></math></span> by the action of <span><math><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> defined by the fixed point free involution <span><math><mo>(</mo><mi>a</mi><mo>,</mo><mi>x</mi><mo>)</mo><mo>↦</mo><mo>(</mo><mo>−</mo><mi>a</mi><mo>,</mo><mi>σ</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>)</mo></math></span>. When X is either a complex Grassmannian manifold <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><msup><mrow><mi>C</mi></mrow><mrow><mi>n</mi></mrow></msup><mo>)</mo></math></span> or a complete flag manifold <span><math><mi>F</mi><mi>ℓ</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span>, we obtain the integral cohomology group of the generalized Dold manifolds <span><math><mi>D</mi><mo>(</mo><mi>m</mi><mo>,</mo><msub><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><msup><mrow><mi>C</mi></mrow><mrow><mi>n</mi></mrow></msup><mo>)</mo><mo>)</mo></math></span> and <span><math><mi>D</mi><mo>(</mo><mi>m</mi><mo>,</mo><mi>F</mi><mi>ℓ</mi><mo>(</mo><mi>n</mi><mo>)</mo><mo>)</mo></math></span> from the well known cell structures of complex Grassmannian and complete flag manifold. Also, we give the rational cohomology of the generalized Dold manifolds <span><math><mi>D</mi><mo>(</mo><mi>m</mi><mo>,</mo><msub><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><msup><mrow><mi>C</mi></mrow><mrow><mi>n</mi></mrow></msup><mo>)</mo><mo>)</mo></math></span> and <span><math><mi>D</mi><mo>(</mo><mi>m</mi><mo>,</mo><mi>F</mi><mi>ℓ</mi><mo>(</mo><mi>n</mi><mo>)</mo><mo>)</mo></math></span>.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109645"},"PeriodicalIF":0.5,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418099","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}
Pub Date : 2025-10-21DOI: 10.1016/j.topol.2025.109643
Ivan S. Gotchev
<div><div>In 2011, Spadaro improved de Groot's inequality <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>h</mi><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, whenever <em>X</em> is a Hausdorff space, by showing that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, for every Hausdorff space <em>X</em>. Recently, Bella proved that if <em>X</em> is a regular <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-space, then <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span> and he asked if the same inequality holds true for every Hausdorff space <em>X</em>. In this paper, for every Hausdorff space <em>X</em> we show that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, and for every Urysohn space <em>X</em>, we prove that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>. Since for regular <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-spaces <em>X</em> we have <span><math><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><mo>=</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><mo>=</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span>, and for every Urysohn space <em>X</em> we have <span><math><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span> and <span><math><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo
{"title":"Strengthening of de Groot's, Spadaro's, and Bella's inequalities for Urysohn spaces","authors":"Ivan S. Gotchev","doi":"10.1016/j.topol.2025.109643","DOIUrl":"10.1016/j.topol.2025.109643","url":null,"abstract":"<div><div>In 2011, Spadaro improved de Groot's inequality <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>h</mi><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, whenever <em>X</em> is a Hausdorff space, by showing that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, for every Hausdorff space <em>X</em>. Recently, Bella proved that if <em>X</em> is a regular <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-space, then <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span> and he asked if the same inequality holds true for every Hausdorff space <em>X</em>. In this paper, for every Hausdorff space <em>X</em> we show that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>, and for every Urysohn space <em>X</em>, we prove that <span><math><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span>. Since for regular <span><math><msub><mrow><mi>T</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-spaces <em>X</em> we have <span><math><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><mo>=</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><mo>=</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span>, and for every Urysohn space <em>X</em> we have <span><math><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>3</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>F</mi><mo>(</mo><mi>X</mi><mo>)</mo><mi>ψ</mi><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup></math></span> and <span><math><mi>h</mi><mi>L</mi><msup><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>θ</mi></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo><msub><mrow><mi>ψ</mi></mrow><mrow><mn>4</mn></mrow></msub><mo>(</mo><mi>X</mi><mo>)</mo></mrow></msup><mo>≤</mo><msup><mrow><mn>2</mn></mrow><mrow><mi>L</mi><mo>(</mo><mi>X</mi><mo","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109643"},"PeriodicalIF":0.5,"publicationDate":"2025-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418013","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}
Pub Date : 2025-10-20DOI: 10.1016/j.topol.2025.109640
Evgenii Reznichenko, Ol'ga Sipacheva
The problem of the existence of non-pseudo--compact -factorizable groups is studied. It is proved that any such group is submetrizable and has weight larger than . Closely related results concerning the -factorizability of products of topological groups and spaces are also obtained (a product of topological spaces is said to be -factorizable if any continuous function factors through a product of maps from X and Y to second-countable spaces). In particular, it is proved that the square of a topological group G is -factorizable as a group if and only if it is -factorizable as a product of spaces, in which case G is pseudo--compact. It is also proved that if the product of a space X and an uncountable discrete space is -factorizable, then is hereditarily separable and hereditarily Lindelöf.
{"title":"Weird R-factorizable groups","authors":"Evgenii Reznichenko, Ol'ga Sipacheva","doi":"10.1016/j.topol.2025.109640","DOIUrl":"10.1016/j.topol.2025.109640","url":null,"abstract":"<div><div>The problem of the existence of non-pseudo-<span><math><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact <span><math><mi>R</mi></math></span>-factorizable groups is studied. It is proved that any such group is submetrizable and has weight larger than <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>. Closely related results concerning the <span><math><mi>R</mi></math></span>-factorizability of products of topological groups and spaces are also obtained (a product <span><math><mi>X</mi><mo>×</mo><mi>Y</mi></math></span> of topological spaces is said to be <span><math><mi>R</mi></math></span>-factorizable if any continuous function <span><math><mi>X</mi><mo>×</mo><mi>Y</mi><mo>→</mo><mi>R</mi></math></span> factors through a product of maps from <em>X</em> and <em>Y</em> to second-countable spaces). In particular, it is proved that the square <span><math><mi>G</mi><mo>×</mo><mi>G</mi></math></span> of a topological group <em>G</em> is <span><math><mi>R</mi></math></span>-factorizable as a group if and only if it is <span><math><mi>R</mi></math></span>-factorizable as a product of spaces, in which case <em>G</em> is pseudo-<span><math><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact. It is also proved that if the product of a space <em>X</em> and an uncountable discrete space is <span><math><mi>R</mi></math></span>-factorizable, then <span><math><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></math></span> is hereditarily separable and hereditarily Lindelöf.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109640"},"PeriodicalIF":0.5,"publicationDate":"2025-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364654","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}
Pub Date : 2025-10-17DOI: 10.1016/j.topol.2025.109637
Ofelia T. Alas , L. Enrique Gutiérrez-Domínguez , Richard G. Wilson
A space is said to be -compact if every closed and discrete subset is countable. In this paper we study spaces whose topologies are maximal with respect to being -compact and we give characterisations of this property in a number of special cases. We also consider the preservation of -compactness in products.
{"title":"Maximal ω1-compactness","authors":"Ofelia T. Alas , L. Enrique Gutiérrez-Domínguez , Richard G. Wilson","doi":"10.1016/j.topol.2025.109637","DOIUrl":"10.1016/j.topol.2025.109637","url":null,"abstract":"<div><div>A space is said to be <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact if every closed and discrete subset is countable. In this paper we study spaces whose topologies are maximal with respect to being <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compact and we give characterisations of this property in a number of special cases. We also consider the preservation of <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>-compactness in products.</div></div>","PeriodicalId":51201,"journal":{"name":"Topology and its Applications","volume":"377 ","pages":"Article 109637"},"PeriodicalIF":0.5,"publicationDate":"2025-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145364653","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}