属于D空间的Box和nabla产品

Pub Date : 2023-05-03 DOI:10.1016/j.indag.2023.04.002
H.A. Barriga-Acosta , P.M. Gartside
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The box product, <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>, is <span><math><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></math></span> with topology generated by all <span><math><mrow><msub><mrow><mo>∏</mo></mrow><mrow><mi>n</mi></mrow></msub><msub><mrow><mi>U</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></math></span>, where every <span><math><msub><mrow><mi>U</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> is open. The nabla product, <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>, is obtained from <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> by quotienting out mod-finite. The weight of <span><math><mi>X</mi></math></span>, <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow></mrow></math></span>, is the minimal size of a base, while <span><math><mrow><mi>d</mi><mo>=</mo><mo>cof</mo><msup><mrow><mi>ω</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>.</p><p>It is shown that there are specific compact spaces <span><math><mi>X</mi></math></span> such that <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> and <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> are not <span><math><mi>D</mi></math></span>, but in general:</p><p>(1) <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> and <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> are hereditarily <span><math><mi>D</mi></math></span> if <span><math><mi>X</mi></math></span> is scattered and either hereditarily paracompact or of finite scattered height, or if <span><math><mi>X</mi></math></span> is metrizable (and <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><mi>d</mi></mrow></math></span> for <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>);</p><p>(2) <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> is hereditarily <span><math><mi>D</mi></math></span> if <span><math><mi>X</mi></math></span> is first countable and <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>, or <em>consistently</em> if <span><math><mi>X</mi></math></span> is first countable and <span><math><mrow><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>c</mi></mrow></math></span>, or <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>; and</p><p>(3) <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> is <span><math><mi>D</mi></math></span> <em>consistently</em> if <span><math><mi>X</mi></math></span> is compact and either first countable or <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>.</p></div>","PeriodicalId":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Box and nabla products that are D-spaces\",\"authors\":\"H.A. 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The box product, <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>, is <span><math><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></math></span> with topology generated by all <span><math><mrow><msub><mrow><mo>∏</mo></mrow><mrow><mi>n</mi></mrow></msub><msub><mrow><mi>U</mi></mrow><mrow><mi>n</mi></mrow></msub></mrow></math></span>, where every <span><math><msub><mrow><mi>U</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> is open. The nabla product, <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>, is obtained from <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> by quotienting out mod-finite. The weight of <span><math><mi>X</mi></math></span>, <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow></mrow></math></span>, is the minimal size of a base, while <span><math><mrow><mi>d</mi><mo>=</mo><mo>cof</mo><msup><mrow><mi>ω</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>.</p><p>It is shown that there are specific compact spaces <span><math><mi>X</mi></math></span> such that <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> and <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> are not <span><math><mi>D</mi></math></span>, but in general:</p><p>(1) <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> and <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> are hereditarily <span><math><mi>D</mi></math></span> if <span><math><mi>X</mi></math></span> is scattered and either hereditarily paracompact or of finite scattered height, or if <span><math><mi>X</mi></math></span> is metrizable (and <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><mi>d</mi></mrow></math></span> for <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span>);</p><p>(2) <span><math><mrow><mo>∇</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> is hereditarily <span><math><mi>D</mi></math></span> if <span><math><mi>X</mi></math></span> is first countable and <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>, or <em>consistently</em> if <span><math><mi>X</mi></math></span> is first countable and <span><math><mrow><mo>|</mo><mi>X</mi><mo>|</mo><mo>≤</mo><mi>c</mi></mrow></math></span>, or <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>; and</p><p>(3) <span><math><mrow><mo>□</mo><msup><mrow><mi>X</mi></mrow><mrow><mi>ω</mi></mrow></msup></mrow></math></span> is <span><math><mi>D</mi></math></span> <em>consistently</em> if <span><math><mi>X</mi></math></span> is compact and either first countable or <span><math><mrow><mi>w</mi><mrow><mo>(</mo><mi>X</mi><mo>)</mo></mrow><mo>≤</mo><msub><mrow><mi>ω</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></math></span>.</p></div>\",\"PeriodicalId\":0,\"journal\":{\"name\":\"\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.0,\"publicationDate\":\"2023-05-03\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0019357723000381\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0019357723000381","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0

摘要

空间X是D,如果对于X中每个点X的开邻域的每一个赋值U,都有一个闭的离散D,使得⋃{U(X):X∈D}=X。盒子产品,□Xω,是拓扑由所有πnUn生成的Xω,其中每个Un是开的。nabla乘积,ŞXω,由□Xω的模有限商。X的权重w(X)是基的最小大小,而d=cofω。证明了存在特定的紧致空间X,使得□Xω和ŞXω不是D,但一般来说:(1)□如果X是散射的并且是可遗传的仿紧的或者是有限散射高度的,或者如果X是可度量的(并且w(X)≤D□Xω);(2) 如果X是第一可数且w(X)≤ω1,或一致地如果X是一可数且|X|≤c,或w(X;和(3)□如果X是紧致的并且是第一可数的或者w(X)≤ω1,则Xω一致为D。
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Box and nabla products that are D-spaces

A space X is D if for every assignment, U, of an open neighborhood to each point x in X there is a closed discrete D such that {U(x):xD}=X. The box product, Xω, is Xω with topology generated by all nUn, where every Un is open. The nabla product, Xω, is obtained from Xω by quotienting out mod-finite. The weight of X, w(X), is the minimal size of a base, while d=cofωω.

It is shown that there are specific compact spaces X such that Xω and Xω are not D, but in general:

(1) Xω and Xω are hereditarily D if X is scattered and either hereditarily paracompact or of finite scattered height, or if X is metrizable (and w(X)d for Xω);

(2) Xω is hereditarily D if X is first countable and w(X)ω1, or consistently if X is first countable and |X|c, or w(X)ω1; and

(3) Xω is D consistently if X is compact and either first countable or w(X)ω1.

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