English

Projective Wellorders and the Nonstationary Ideal

Logic 2016-10-14 v1

Abstract

We show that, under the assumption of the existence of M1#M_1^{\#}, there exists a model on which the restricted nonstationary ideal NSA\hbox{NS} \upharpoonright A is 2\aleph_2-saturated, for AA a stationary co-stationary subset of ω1\omega_1, while the full nonstationary ideal NS\hbox{NS} can be made Δ1\Delta_1 definable with Kω1K_{\omega_1} as a parameter. Further we show, again under the assumption of the existence of M1#M_1^{\#} that there is a model of set theory such that NS\hbox{NS} is 2\aleph_2-saturated and such that there is lightface Σ41\Sigma^1_4-definable well-order on the reals. This result is optimal in the presence of a measurable cardinal.

Keywords

Cite

@article{arxiv.1610.04039,
  title  = {Projective Wellorders and the Nonstationary Ideal},
  author = {Stefan Hoffelner},
  journal= {arXiv preprint arXiv:1610.04039},
  year   = {2016}
}

Comments

This is the authors PhD thesis

R2 v1 2026-06-22T16:19:41.834Z