{"title":"一个被遗忘的Pełczyński定理:$(\\lambda +)$-内射空间不一定是$\\lambda $-内射- $\\lambda \\in(1,2)$的情况","authors":"Tomasz Kania, G. Lewicki","doi":"10.4064/sm220119-25-6","DOIUrl":null,"url":null,"abstract":". Isbell and Semadeni [Trans. Amer. Math. Soc. 107 (1963)] proved that every infinite-dimensional 1-injective Banach space contains a hyperplane that is (2+ ε )-injective for every ε > 0, yet is is not 2-injective and remarked in a footnote that Pe lczy´nski had proved for every λ > 1 the existence of a ( λ + ε )-injective space ( ε > 0) that is not λ injective. Unfortunately, no trace of the proof of Pe lczy´nski’s result has been preserved. In the present paper, we establish the said theorem for λ ∈ (1 , 2] by constructing an appropriate renorming of ℓ ∞ . This contrasts (at least for real scalars) with the case λ = 1 for which Lindenstrauss [Mem. Amer. Math. Soc. 48 (1964)] proved the contrary statement.","PeriodicalId":51179,"journal":{"name":"Studia Mathematica","volume":" ","pages":""},"PeriodicalIF":0.7000,"publicationDate":"2022-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A forgotten theorem of Pełczyński: $(\\\\lambda +)$-injective spaces need not be $\\\\lambda $-injective—the case $\\\\lambda \\\\in (1,2]$\",\"authors\":\"Tomasz Kania, G. Lewicki\",\"doi\":\"10.4064/sm220119-25-6\",\"DOIUrl\":null,\"url\":null,\"abstract\":\". Isbell and Semadeni [Trans. Amer. Math. Soc. 107 (1963)] proved that every infinite-dimensional 1-injective Banach space contains a hyperplane that is (2+ ε )-injective for every ε > 0, yet is is not 2-injective and remarked in a footnote that Pe lczy´nski had proved for every λ > 1 the existence of a ( λ + ε )-injective space ( ε > 0) that is not λ injective. Unfortunately, no trace of the proof of Pe lczy´nski’s result has been preserved. In the present paper, we establish the said theorem for λ ∈ (1 , 2] by constructing an appropriate renorming of ℓ ∞ . This contrasts (at least for real scalars) with the case λ = 1 for which Lindenstrauss [Mem. Amer. Math. Soc. 48 (1964)] proved the contrary statement.\",\"PeriodicalId\":51179,\"journal\":{\"name\":\"Studia Mathematica\",\"volume\":\" \",\"pages\":\"\"},\"PeriodicalIF\":0.7000,\"publicationDate\":\"2022-01-19\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Studia Mathematica\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.4064/sm220119-25-6\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Studia Mathematica","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.4064/sm220119-25-6","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
A forgotten theorem of Pełczyński: $(\lambda +)$-injective spaces need not be $\lambda $-injective—the case $\lambda \in (1,2]$
. Isbell and Semadeni [Trans. Amer. Math. Soc. 107 (1963)] proved that every infinite-dimensional 1-injective Banach space contains a hyperplane that is (2+ ε )-injective for every ε > 0, yet is is not 2-injective and remarked in a footnote that Pe lczy´nski had proved for every λ > 1 the existence of a ( λ + ε )-injective space ( ε > 0) that is not λ injective. Unfortunately, no trace of the proof of Pe lczy´nski’s result has been preserved. In the present paper, we establish the said theorem for λ ∈ (1 , 2] by constructing an appropriate renorming of ℓ ∞ . This contrasts (at least for real scalars) with the case λ = 1 for which Lindenstrauss [Mem. Amer. Math. Soc. 48 (1964)] proved the contrary statement.
期刊介绍:
The journal publishes original papers in English, French, German and Russian, mainly in functional analysis, abstract methods of mathematical analysis and probability theory.