English

Forcing More DC Over the Chang Model Using the Thorn Sequence

Logic 2024-04-01 v3

Abstract

In the context of ZF+DC\mathsf{ZF}+\mathsf{DC}, we force DCκ\mathsf{DC}_\kappa for relations on P(κ)\mathcal{P}(\kappa) for κ<ω\kappa{}<\aleph_\omega over the Chang model L(Ordω)\mathrm{L}(\mathrm{Ord}^\omega) making some assumptions on the thorn sequence defined by \unicodexFE0=ω{\it \unicode{xFE}}_0=\omega, \unicodexFEα+1{\it \unicode{xFE}}_{\alpha{}+1} as the least ordinal not a surjective image of \unicodexFEαω{\it \unicode{xFE}}_\alpha^\omega (i.e. no f:\unicodexFEαω\unicodexFEα+1f:{\it \unicode{xFE}}_{\alpha}^\omega{}\rightarrow {\it \unicode{xFE}}_{\alpha{}+1} is surjective) and \unicodexFEγ=supα<γ\unicodexFEα{\it \unicode{xFE}}_\gamma{}=\sup_{\alpha{}<\gamma}{\it \unicode{xFE}}_\alpha for limit γ\gamma. These assumptions are motivated from results about Θ\Theta in the context of determinacy, and could be reasonable ways of thinking about the Chang model. Explicitly, we assume cardinals λ\lambda on the thorn sequence are strongly regular (meaning regular and functions f:κ<κλf:\kappa{}^{<\kappa}\rightarrow \lambda are bounded whenever κ<λ\kappa{}<\lambda is on the thorn sequence) and justified (meaning P(κω)L(Ordω)Lλ(λω,X)\mathcal{P}(\kappa^\omega)\cap \mathrm{L}(\mathrm{Ord}^\omega)\subseteq \mathrm{L}_{\lambda}(\lambda^\omega{},X) for some XλX\subseteq \lambda for any κ<λ\kappa{}<\lambda on the thorn sequence). This allow us to use Cohen forcing and establish more dependent choice.

Keywords

Cite

@article{arxiv.2210.16359,
  title  = {Forcing More DC Over the Chang Model Using the Thorn Sequence},
  author = {James Holland and Grigor Sargsyan},
  journal= {arXiv preprint arXiv:2210.16359},
  year   = {2024}
}
R2 v1 2026-06-28T04:44:37.608Z