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arXiv · 2112.00366

Some remarks on contractive and existence sets

Maciej Ciesielski·Grzegorz Lewicki
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Abstract

Let X be a real or complex Banach space and let F in X be a non-empty set. F is called an existence set of best coapproximation (existence set for brevity), if for any x in X, $R_F(x)$ is not the empty set, where $$ R_F (x) = \{ d \in F : \|d-c\| \leq \|x-c\| \hbox{ for any } c \in F \}.$$ It is clear that any existence set is a contractive subset of X. The aim of this paper is to present some conditions on F and X under which the notions of exsistence set and contractive set are equivalent.

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Maciej Ciesielski, Grzegorz Lewicki. 2021-12-01. Some remarks on contractive and existence sets. https://arxiv.org/abs/2112.00366

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