{"title":"局部Blaschke-Kakutani椭球表征与Banach等距子空间问题","authors":"Sergei Ivanov , Daniil Mamaev , Anya Nordskova","doi":"10.1016/j.jfa.2025.111063","DOIUrl":null,"url":null,"abstract":"<div><div>We prove the following local version of Blaschke–Kakutani's characterization of ellipsoids: Let <em>V</em> be a finite-dimensional real vector space, <span><math><mi>B</mi><mo>⊂</mo><mi>V</mi></math></span> a convex body with 0 in its interior, and <span><math><mn>2</mn><mo>≤</mo><mi>k</mi><mo><</mo><mi>dim</mi><mo></mo><mi>V</mi></math></span> an integer. Suppose that the body <em>B</em> is contained in a cylinder based on the cross-section <span><math><mi>B</mi><mo>∩</mo><mi>X</mi></math></span> for every <em>k</em>-plane <em>X</em> from a connected open set of linear <em>k</em>-planes in <em>V</em>. Then in the region of <em>V</em> swept by these <em>k</em>-planes <em>B</em> coincides with either an ellipsoid, or a cylinder over an ellipsoid, or a cylinder over a <em>k</em>-dimensional base.</div><div>For <span><math><mi>k</mi><mo>=</mo><mn>2</mn></math></span> and <span><math><mi>k</mi><mo>=</mo><mn>3</mn></math></span> we obtain as a corollary a local solution to Banach's isometric subspaces problem: If all cross-sections of <em>B</em> by <em>k</em>-planes from a connected open set are linearly equivalent, then the same conclusion as above holds.</div></div>","PeriodicalId":15750,"journal":{"name":"Journal of Functional Analysis","volume":"289 8","pages":"Article 111063"},"PeriodicalIF":1.6000,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Local Blaschke–Kakutani ellipsoid characterization and Banach's isometric subspaces problem\",\"authors\":\"Sergei Ivanov , Daniil Mamaev , Anya Nordskova\",\"doi\":\"10.1016/j.jfa.2025.111063\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>We prove the following local version of Blaschke–Kakutani's characterization of ellipsoids: Let <em>V</em> be a finite-dimensional real vector space, <span><math><mi>B</mi><mo>⊂</mo><mi>V</mi></math></span> a convex body with 0 in its interior, and <span><math><mn>2</mn><mo>≤</mo><mi>k</mi><mo><</mo><mi>dim</mi><mo></mo><mi>V</mi></math></span> an integer. Suppose that the body <em>B</em> is contained in a cylinder based on the cross-section <span><math><mi>B</mi><mo>∩</mo><mi>X</mi></math></span> for every <em>k</em>-plane <em>X</em> from a connected open set of linear <em>k</em>-planes in <em>V</em>. Then in the region of <em>V</em> swept by these <em>k</em>-planes <em>B</em> coincides with either an ellipsoid, or a cylinder over an ellipsoid, or a cylinder over a <em>k</em>-dimensional base.</div><div>For <span><math><mi>k</mi><mo>=</mo><mn>2</mn></math></span> and <span><math><mi>k</mi><mo>=</mo><mn>3</mn></math></span> we obtain as a corollary a local solution to Banach's isometric subspaces problem: If all cross-sections of <em>B</em> by <em>k</em>-planes from a connected open set are linearly equivalent, then the same conclusion as above holds.</div></div>\",\"PeriodicalId\":15750,\"journal\":{\"name\":\"Journal of Functional Analysis\",\"volume\":\"289 8\",\"pages\":\"Article 111063\"},\"PeriodicalIF\":1.6000,\"publicationDate\":\"2025-05-22\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Functional Analysis\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0022123625002459\",\"RegionNum\":2,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Functional Analysis","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0022123625002459","RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATHEMATICS","Score":null,"Total":0}
Local Blaschke–Kakutani ellipsoid characterization and Banach's isometric subspaces problem
We prove the following local version of Blaschke–Kakutani's characterization of ellipsoids: Let V be a finite-dimensional real vector space, a convex body with 0 in its interior, and an integer. Suppose that the body B is contained in a cylinder based on the cross-section for every k-plane X from a connected open set of linear k-planes in V. Then in the region of V swept by these k-planes B coincides with either an ellipsoid, or a cylinder over an ellipsoid, or a cylinder over a k-dimensional base.
For and we obtain as a corollary a local solution to Banach's isometric subspaces problem: If all cross-sections of B by k-planes from a connected open set are linearly equivalent, then the same conclusion as above holds.
期刊介绍:
The Journal of Functional Analysis presents original research papers in all scientific disciplines in which modern functional analysis plays a basic role. Articles by scientists in a variety of interdisciplinary areas are published.
Research Areas Include:
• Significant applications of functional analysis, including those to other areas of mathematics
• New developments in functional analysis
• Contributions to important problems in and challenges to functional analysis