English

Nonmeasurable images

General Topology 2021-12-30 v1

Abstract

In this article we will investigate nonmeasurability with respect to some σ\sigma-ideals in Polish space X,X, of images of subsets of XX by selected mappings defined on the space XX. Among of them we answer the following question: "It is true that there exists a subset of the unit disc in the real plane such that the continuum many projections onto lines are Lebesgue measurable and continuum many projections are not?". It is known that there exists continuous function f:[0,1][0,1]f:[0,1]\to [0,1] such that for every Bernstein set B[0,1]B\subseteq [0,1] we have f[B]=[0,1].f[B]=[0,1]. We show relative consistency with ZFCZFC of fact that the above result is not true for some \cn\cn or \cm\cm-completely nonmeasurable sets, even if we take less than \c many continuous functions.

Keywords

Cite

@article{arxiv.2112.14629,
  title  = {Nonmeasurable images},
  author = {Aleksander Cieślak and Robert Rałowski},
  journal= {arXiv preprint arXiv:2112.14629},
  year   = {2021}
}
R2 v1 2026-06-24T08:34:51.486Z