English

Various notions of best approximation property in spaces of Bochner integrable functions

Functional Analysis 2017-02-03 v4

Abstract

We derive that for a separable proximinal subspace YY of XX, YY is strongly proximinal (strongly ball proximinal) if and only if for 1p<1\leq p< \infty, Lp(I,Y)L_p(I,Y) is strongly proximinal (strongly ball proximinal) in Lp(I,X)L_p(I,X). Case for p=p=\infty follows from stronger assumption on YY in XX (uniform proximinality). It is observed that for a separable proximinal subspace YY in XX, YY is ball proximinal in XX if and only if Lp(I,Y)L_p(I,Y) is ball proximinal in Lp(I,X)L_p(I,X) for 1p1\leq p\leq\infty. Our observations also include the fact that for any (strongly) proximinal subspace YY of XX, if every separable subspace of YY is ball (strongly) proximinal in XX then Lp(I,Y)L_p(I,Y) is ball (strongly) proximinal in Lp(I,X)L_p(I,X) for 1p<1\leq p<\infty. We introduce the notion of uniform proximinality of a closed convex set in a Banach space, which is wrongly defined in \cite{LZ}. Several examples are given having this property, viz. any UU-subspace of a Banach space, closed unit ball BXB_X of a space with 3.2.I.P3.2.I.P, closed unit ball of any M-ideal of a space with 3.2.I.P.3.2.I.P. are uniformly proximinal. A new class of examples are given having this property.

Keywords

Cite

@article{arxiv.1610.03209,
  title  = {Various notions of best approximation property in spaces of Bochner integrable functions},
  author = {Tanmoy Paul},
  journal= {arXiv preprint arXiv:1610.03209},
  year   = {2017}
}

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24 pages