English

Filters, ideal independence and ideal Mr\'owka spaces

Logic 2023-04-11 v1

Abstract

A family A[ω]ω\mathcal{A} \subseteq [\omega]^\omega such that for all finite {Xi}inA\{X_i\}_{i\in n}\subseteq \mathcal A and AA{Xi}inA \in \mathcal{A} \setminus \{X_i\}_{i\in n}, the set AinXiA \setminus \bigcup_{i \in n} X_i is infinite, is said to be ideal independent. We prove that an ideal independent family A\mathcal{A} is maximal if and only if A\mathcal A is J\mathcal J-completely separable and maximal J\mathcal J-almost disjoint for a particular ideal J\mathcal J on ω\omega. We show that usmm\mathfrak{u}\leq\mathfrak{s}_{mm}, where smm\mathfrak{s}_{mm} is the minimal cardinality of maximal ideal independent family. This, in particular, establishes the independence of smm\mathfrak{s}_{mm} and i\mathfrak{i}. Given an arbitrary set CC of uncountable cardinals, we show how to simultaneously adjoin via forcing maximal ideal independent families of cardinality λ\lambda for each λC\lambda\in C, thus establishing the consistency of Cspec(smm)C\subseteq \hbox{spec}(\mathfrak{s}_{mm}). Assuming CH\mathsf{CH}, we construct a maximal ideal independent family, which remains maximal after forcing with any proper, ωω^\omega\omega-bounding, pp-point preserving forcing notion and evaluate smm\mathfrak{s}_{mm} in several well studied forcing extensions. We also study natural filters associated with ideal independence and introduce an analog of Mr\'owka spaces for ideal independent families.

Keywords

Cite

@article{arxiv.2304.04651,
  title  = {Filters, ideal independence and ideal Mr\'owka spaces},
  author = {Serhii Bardyla and Jonathan Cancino-Manríquez and Vera Fischer and Corey Bacal Switzer},
  journal= {arXiv preprint arXiv:2304.04651},
  year   = {2023}
}

Comments

18 Pages, subsumes arXiv:2206.14019