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Smoothness of subspace sections of the unit balls of C(Q) and L1
Journal of Approximation Theory ( IF 0.9 ) Pub Date : 2021-01-23 , DOI: 10.1016/j.jat.2021.105552
A.R. Alimov , I.G. Tsar’kov

We show that, for any integer n2, the space C(Q) (where Q is a Hausdorff compact set, card Q>n) contains an n-dimensional subspace such that any translation thereof by a vector p, p<1, intersects the unit ball B of C(Q) in a nonsmooth set. In L1[0,1], we show that if is an arbitrary finite-dimensional subspace in L1[0,1], dim1, then there exists a dense set in the unit ball BL1[0,1] set of its translations that intersect the unit ball of L1[0,1] in smooth sets. As an application, we show that in L1[0,1] any finite-dimensional sun is convex. This extends the classical P. Ørno–Yu. A. Brudnyi–E. A. Gorin’s theorem to the effect that in L1[0,1] any Chebyshev set is either a singleton or is infinite-dimensional.



中文翻译:

单位球的子空间部分的光滑度 C大号1个

我们证明,对于任何整数 ñ2, 空间 C (哪里  是Hausdorff紧凑套装, >ñ)包含一个 ñ维子空间,以使其通过向量进行任何平移 pp<1个,与单位球相交  的 C在不光滑的环境中。在大号1个[01个],我们证明 是一个任意的有限维子空间 大号1个[01个]暗淡1个,那么在单位球中存在一个密集的集合 大号1个[01个] 一组与单位球相交的翻译 大号1个[01个]在顺利的情况下。作为应用程序,我们在大号1个[01个]任何有限维的太阳都是凸的。这扩展了经典的P. Ørno–Yu。 答:布吕迪尼-E。 A. Gorin定理的作用是大号1个[01个] 任何Chebyshev集都可以是单例或无穷大。

更新日期:2021-02-04
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