Common fixed points and invariant approximation of R-subweakly commuting maps in convex metric spaces

Sufficient conditions for the existence of a common fixed point of R-subweakly commuting mappings are established within the framework of a convex metric space. As applications, we obtain various results on the best approximation for this class of mappings generalizing the results known from the literature.Встановлено достатні умови існування спільної нерухомої точки R-субслабко комутуючих відображень у рамках опуклого метричного простору. Як застосування, одержано різні результати щодо найкращих наближень для згаданого класу відображень, які узагальнюють інші відомі з літератури результати

A look at proximinal and Chebyshev sets in Banach spaces

The main aim of this survey is to present some classical as well asrecent characterizations involving the notion of proximinal and Chebyshev sets inBanach spaces. In particular, we discuss the convexity of Chebyshev sets

A Note on The Convexity of Chebyshev Sets

Perhaps one of the major unsolved problem in Approximation Theoryis: Whether or not every Chebyshev subset of a Hilbert space must be convex. Many partial answers to this problem are available in the literature. R.R. Phelps[Proc. Amer. Math. Soc. 8 (1957), 790-797] showed that a Chebyshev set in an inner product space (or in a strictly convex normed linear space) is convex if the associated metric projection is non-expansive. We extend this result to metricspaces