English

Non-Normal Magidor-Radin Types of Forcings

Logic 2024-05-28 v1

Abstract

We develop the non-normal variations of two classical Prikry-type forcings; namely, Magidor and Radin forcings. We generalize the fact that the non-normal Prikry forcing is a projection of the extender-based to a coordinate of the extender to our forcing and the Radin/Magidor-Radin-extender-based forcing from \cite{CarmiMagidorRadin,CarmiRadin}. Then, we show that both the non-normal variation of Magidor and Radin forcings can add a Cohen generic function to every limit point of cofinality ω\omega of the generic club. Second, we show that this phenomenon is limited to the cases where the forcings are not designed to change the cofinality of a measurable κ\kappa to ω1\omega_1. Specifically, in the above-mentioned circumstances these forcings do not project onto any κ\kappa-distributive forcing. We use that to conclude that the extender-based Radin/Magidor-Radin forcing does not add fresh subsets to κ\kappa as well. In the second part of the paper we focus on the natural non-normal variation of Gitik's forcing from \cite[\S3]{GitikNonStationary}. Our main result shows that this poset can be employed to change the cofinality of a measurable cardinal κ\kappa to ω1\omega_1 while introducing a Cohen subset of κ\kappa.

Keywords

Cite

@article{arxiv.2405.16704,
  title  = {Non-Normal Magidor-Radin Types of Forcings},
  author = {Tom Benhamou and Alejandro Poveda},
  journal= {arXiv preprint arXiv:2405.16704},
  year   = {2024}
}