$\alpha$-limit of scalar-valued functions and related Banach spaces

Authors

  • Ali Bayati Eshkaftaki Author
  • Martin Ljubenovic University of Nis Author

DOI:

https://doi.org/10.2298/FIL2607543E

Abstract

In this paper, for a set $X,$ a scalar valued function $f:X\rightarrow\Bbb F,$ where $\Bbb F$ is assumed to be the set of all real or complex numbers, and for a cardinal number $\alpha,$ we define the $\alpha$-limit of $f$ as a generalization of the limit of a sequence and denote it by $\lim^{\alpha} f.$ Indeed, if we assume that $\alpha=\aleph_0$ and $X=\Bbb N,$ then $\lim^{\alpha} f$ is equal to $\lim_{n\to \infty}f(n).$ If $X$ is an infinite set and $\alpha$ an infinite cardinal number, then we define two classes of Banach spaces ${\mathfrak c}_0^{\alpha}(X)$ and ${\mathfrak c}^{\alpha}(X)$ containing all bounded functions $f:X \to \Bbb F$ which satisfy $\lim^{\alpha} f =0$ and that $\lim^{\alpha} f$ exists, respectively. Then we show that ${\mathfrak c}_0(X)\subseteq {\mathfrak c}_0^{\alpha}(X)\subseteq \ell^{\infty}(X)$ and ${\mathfrak c}(X)\subseteq {\mathfrak c}^{\alpha}(X)\subseteq \ell^{\infty}(X).$ Also, whenever the cardinal number $\alpha$ increases these spaces become larger such that the equality hold on the left sides for $\alpha =\aleph_0$ and on the right sides for all $\alpha>\card(X).$

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Published

2026-03-30

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Section

Articles