Capturing sets of ordinals by normal ultrapowers
Logic
2023-02-28 v5
Abstract
We investigate the extent to which ultrapowers by normal measures on can be correct about powersets for . We consider two versions of this questions, the capturing property and the local capturing property . holds if there is an ultrapower by a normal measure on which correctly computes . is a weakening of which holds if every subset of is contained in some ultrapower by a normal measure on . After examining the basic properties of these two notions, we identify the exact consistency strength of . Building on results of Cummings, who determined the exact consistency strength of , and using a forcing due to Apter and Shelah, we show that can hold at the least measurable cardinal.
Keywords
Cite
@article{arxiv.1902.10638,
title = {Capturing sets of ordinals by normal ultrapowers},
author = {Miha E. Habič and Radek Honzík},
journal= {arXiv preprint arXiv:1902.10638},
year = {2023}
}
Comments
31 pages; corrected typos