English

Maximal almost disjoint families, determinacy, and forcing

Logic 2022-10-07 v1

Abstract

We study the notion of J\mathcal J-MAD families where J\mathcal J is a Borel ideal on ω\omega. We show that if J\mathcal J is an arbitrary FσF_\sigma ideal, or is any finite or countably iterated Fubini product of FσF_\sigma ideals, then there are no analytic infinite J\mathcal J-MAD families, and assuming Projective Determinacy there are no infinite projective J\mathcal J-MAD families; and under the full Axiom of Determinacy + V=L(R)V=\mathbf{L}(\mathbb{R}) there are no infinite J\mathcal J-mad families. These results apply in particular when J\mathcal J is the ideal of finite sets Fin\mathrm{Fin}, which corresponds to the classical notion of MAD families. The proofs combine ideas from invariant descriptive set theory and forcing.

Cite

@article{arxiv.1810.03016,
  title  = {Maximal almost disjoint families, determinacy, and forcing},
  author = {Karen Bakke Haga and David Schrittesser and Asger Törnquist},
  journal= {arXiv preprint arXiv:1810.03016},
  year   = {2022}
}

Comments

40 pages

R2 v1 2026-06-23T04:30:39.685Z