English

Compactness versus hugeness at successor cardinals

Logic 2020-10-01 v1

Abstract

If κ\kappa is regular and 2<κκ+2^{<\kappa}\leq\kappa^+, then the existence of a weakly presaturated ideal on κ+\kappa^+ implies κ\square^*_\kappa. This partially answers a question of Foreman and Magidor about the approachability ideal on ω2\omega_2. As a corollary, we show that if there is a presaturated ideal II on ω2\omega_2 such that P(ω2)/I\mathcal{P}(\omega_2)/I is semiproper, then CH holds. We also show some barriers to getting the tree property and a saturated ideal simultaneously on a successor cardinal from conventional forcing methods.

Keywords

Cite

@article{arxiv.2009.14245,
  title  = {Compactness versus hugeness at successor cardinals},
  author = {Sean Cox and Monroe Eskew},
  journal= {arXiv preprint arXiv:2009.14245},
  year   = {2020}
}