{"title":"关于可数完全贫乏集和可数完全空集","authors":"Tomasz Weiss , Piotr Zakrzewski","doi":"10.1016/j.apal.2023.103357","DOIUrl":null,"url":null,"abstract":"<div><p>We study a strengthening of the notion of a universally meager set and its dual counterpart that strengthens the notion of a universally null set.</p><p>We say that a subset <em>A</em> of a perfect Polish space <em>X</em> is countably perfectly meager (respectively, countably perfectly null) in <em>X</em>, if for every perfect Polish topology <em>τ</em> on <em>X</em>, giving the original Borel structure of <em>X</em>, <em>A</em> is covered by an <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span>-set <em>F</em> in <em>X</em> with the original Polish topology such that <em>F</em> is meager with respect to <em>τ</em> (respectively, for every finite, non-atomic, Borel measure <em>μ</em> on <em>X</em>, <em>A</em> is covered by an <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span>-set <em>F</em> in <em>X</em> with <span><math><mi>μ</mi><mo>(</mo><mi>F</mi><mo>)</mo><mo>=</mo><mn>0</mn></math></span>).</p><p>We prove that if <span><math><msup><mrow><mn>2</mn></mrow><mrow><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup><mo>≤</mo><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, then there exists a universally meager set in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> which is not countably perfectly meager in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> (respectively, a universally null set in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> which is not countably perfectly null in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span>).</p></div>","PeriodicalId":50762,"journal":{"name":"Annals of Pure and Applied Logic","volume":"175 1","pages":"Article 103357"},"PeriodicalIF":0.6000,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"On countably perfectly meager and countably perfectly null sets\",\"authors\":\"Tomasz Weiss , Piotr Zakrzewski\",\"doi\":\"10.1016/j.apal.2023.103357\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>We study a strengthening of the notion of a universally meager set and its dual counterpart that strengthens the notion of a universally null set.</p><p>We say that a subset <em>A</em> of a perfect Polish space <em>X</em> is countably perfectly meager (respectively, countably perfectly null) in <em>X</em>, if for every perfect Polish topology <em>τ</em> on <em>X</em>, giving the original Borel structure of <em>X</em>, <em>A</em> is covered by an <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span>-set <em>F</em> in <em>X</em> with the original Polish topology such that <em>F</em> is meager with respect to <em>τ</em> (respectively, for every finite, non-atomic, Borel measure <em>μ</em> on <em>X</em>, <em>A</em> is covered by an <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>σ</mi></mrow></msub></math></span>-set <em>F</em> in <em>X</em> with <span><math><mi>μ</mi><mo>(</mo><mi>F</mi><mo>)</mo><mo>=</mo><mn>0</mn></math></span>).</p><p>We prove that if <span><math><msup><mrow><mn>2</mn></mrow><mrow><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup><mo>≤</mo><msub><mrow><mi>ℵ</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, then there exists a universally meager set in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> which is not countably perfectly meager in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> (respectively, a universally null set in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span> which is not countably perfectly null in <span><math><msup><mrow><mn>2</mn></mrow><mrow><mi>N</mi></mrow></msup></math></span>).</p></div>\",\"PeriodicalId\":50762,\"journal\":{\"name\":\"Annals of Pure and Applied Logic\",\"volume\":\"175 1\",\"pages\":\"Article 103357\"},\"PeriodicalIF\":0.6000,\"publicationDate\":\"2023-08-29\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Annals of Pure and Applied Logic\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0168007223001148\",\"RegionNum\":2,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"LOGIC\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Annals of Pure and Applied Logic","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0168007223001148","RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"LOGIC","Score":null,"Total":0}
On countably perfectly meager and countably perfectly null sets
We study a strengthening of the notion of a universally meager set and its dual counterpart that strengthens the notion of a universally null set.
We say that a subset A of a perfect Polish space X is countably perfectly meager (respectively, countably perfectly null) in X, if for every perfect Polish topology τ on X, giving the original Borel structure of X, A is covered by an -set F in X with the original Polish topology such that F is meager with respect to τ (respectively, for every finite, non-atomic, Borel measure μ on X, A is covered by an -set F in X with ).
We prove that if , then there exists a universally meager set in which is not countably perfectly meager in (respectively, a universally null set in which is not countably perfectly null in ).
期刊介绍:
The journal Annals of Pure and Applied Logic publishes high quality papers in all areas of mathematical logic as well as applications of logic in mathematics, in theoretical computer science and in other related disciplines. All submissions to the journal should be mathematically correct, well written (preferably in English)and contain relevant new results that are of significant interest to a substantial number of logicians. The journal also considers submissions that are somewhat too long to be published by other journals while being too short to form a separate memoir provided that they are of particular outstanding quality and broad interest. In addition, Annals of Pure and Applied Logic occasionally publishes special issues of selected papers from well-chosen conferences in pure and applied logic.