English

Small infinite partitions and other features of the Nowhere Centered ideal

Logic 2022-03-02 v1

Abstract

The \textit{nowhere dense ideal} NC\mathcal{NC} is introduced. It is a coanalytic ideal of ω×ω\omega\times\omega whose defining characteristic is that the sets of the form X×YX\times Y, where X,YX,Y are infinite subsets of ω\omega, are dense in the quotient P(ω×ω)\slashNC\mathcal{P}(\omega\times\omega)\slash\mathcal{NC}. This quotient has countable partitions and consistently has partitions of size ω1\omega_1 while a>ω1\mathfrak{a}>\omega_1. This represents a huge contrast with other definable quotients. Other combinatorial features of this ideal are presented, as well as some results on a family of similar, higher dimensional ideals.

Keywords

Cite

@article{arxiv.2203.00234,
  title  = {Small infinite partitions and other features of the Nowhere Centered ideal},
  author = {Mario Jardón Santos},
  journal= {arXiv preprint arXiv:2203.00234},
  year   = {2022}
}