English

Bounded ranges of cardinal functions

Classical Analysis and ODEs 2025-08-19 v1 Combinatorics

Abstract

Let x\mathbf{x} be a (non-empty) sequence of positive real numbers. Its achievement set x\mathcal{\mathbf{x}} is the set of all the possible sums of the elements of x\mathbf{x}. The cardinal function of x\mathbf{x} is the function f:A(x)N{ω,c}f:\mathcal{A}(\mathbf{x}) \to \mathbb{N}\cup\{\omega,\mathfrak{c}\} that for every xA(x)x\in\mathbb{A}(\mathbf{x}) the value f(x)f(x) is equal to the number of ways xx is represented as a sum of elements of x\mathbf{x}. In this paper we consider possible ranges of cardinal functions of sequences x\mathbf{x}. We present some general constructions and several criteria that a set has to satisfy in order to be a range of a cardinal function. We put special attention to the case of sets with maximal element equal to 66. In this case, in particular, we obtained a full characterisation of sets that are ranges of cardinal functions of interval-filling sequences.

Keywords

Cite

@article{arxiv.2508.13016,
  title  = {Bounded ranges of cardinal functions},
  author = {Jacek Marchwicki and Błażej Żmija},
  journal= {arXiv preprint arXiv:2508.13016},
  year   = {2025}
}
R2 v1 2026-07-01T04:55:00.826Z