Approach to the density ideal by density of special testing sets on the real line

It is known that a set A ⊂ ℕ belongs to the density ideal $$\mathcal{Z}$$ if and only if zero is a dispersion point of a specific interval subset of ℝ defined for the sequence 1/n, namely, of the set $${\bigcup }_{i\in A}\left[1/\left(i+1\right),1/i\right].$$ We investigate here for which decreasing sequences (xn) tending to zero the analogous equivalence holds, that is, for which sequences A ∈ $$\mathcal{Z}$$ if and only if zero is a dispersion point of $${\bigcup }_{i\in A}\left[{x}_{i+1},{x}_{i}\right].$$

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Publication Details

Journal
Lithuanian Mathematical Journal
Published
2025-10-01
DOI
https://doi.org/10.1007/s10986-025-09696-w
Primary Topic
Approximation Theory and Sequence Spaces
Type
article
Field-Weighted Citation Impact
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article

Approach to the density ideal by density of special testing sets on the real line

Tomasz Filipczak, Gražyna Horbaczewska, Małgorzata Filipczak
Lithuanian Mathematical Journal
Approximation Theory and Sequence Spaces
article

Approach to the density ideal by density of special testing sets on the real line

Tomasz Filipczak, Gražyna Horbaczewska, Małgorzata Filipczak
article en

Abstract

It is known that a set A ⊂ ℕ belongs to the density ideal $$\mathcal{Z}$$ if and only if zero is a dispersion point of a specific interval subset of ℝ defined for the sequence 1/n, namely, of the set $${\bigcup }_{i\in A}\left[1/\left(i+1\right),1/i\right].$$ We investigate here for which decreasing sequences (xn) tending to zero the analogous equivalence holds, that is, for which sequences A ∈ $$\mathcal{Z}$$ if and only if zero is a dispersion point of $${\bigcup }_{i\in A}\left[{x}_{i+1},{x}_{i}\right].$$

Lithuanian Mathematical JournalVol. 65(4)
Lodz University of Technology (PL), University of Łódź (PL)
Openalex Percentile: Top 68%
Approximation Theory and Sequence Spaces
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