English

Tree forcing and definable maximal independent sets in hypergraphs

Logic 2022-04-26 v2

Abstract

We show that after forcing with a countable support iteration or a finite product of Sacks or splitting forcing over LL, every analytic hypergraph on a Polish space admits a Δ21\mathbf{\Delta}^1_2 maximal independent set. As a main application we get the consistency of r=u=i=ω2\mathfrak{r} = \mathfrak{u} = \mathfrak{i} = \omega_2 together with the existence of a Δ21\Delta^1_2 ultrafilter, a Π11\Pi^1_1 maximal independent family and a Δ21\Delta^1_2 Hamel basis. This solves open problems of Brendle, Fischer and Khomskii and the author. We also show in ZFC that dicl\mathfrak{d} \leq \mathfrak{i}_{cl}.

Keywords

Cite

@article{arxiv.2009.06445,
  title  = {Tree forcing and definable maximal independent sets in hypergraphs},
  author = {Jonathan Schilhan},
  journal= {arXiv preprint arXiv:2009.06445},
  year   = {2022}
}
R2 v1 2026-06-23T18:31:30.352Z