English

A Mitchell-like order for Ramsey and Ramsey-like cardinals

Logic 2021-05-14 v1

Abstract

Smallish large cardinals κ\kappa are often characterized by the existence of a collection of filters on κ\kappa, each of which is an ultrafilter on the subsets of κ\kappa of some transitive ZFC\mathrm{ZFC}^--model of size κ \kappa. We introduce a Mitchell-like order for Ramsey and Ramsey-like cardinals, ordering such collections of small filters. We show that the Mitchell-like order and the resulting notion of rank have all the desirable properties of the Mitchell order on normal measures on a measurable cardinal. The Mitchell-like order behaves robustly with respect to forcing constructions. We show that extensions with cover and approximation properties cannot increase the rank of a Ramsey or Ramsey-like cardinal. We use the results about extensions with cover and approximation properties together with recently developed techniques about soft killing of large-cardinal degrees by forcing to softly kill the ranks of Ramsey and Ramsey-like cardinals.

Keywords

Cite

@article{arxiv.1609.07645,
  title  = {A Mitchell-like order for Ramsey and Ramsey-like cardinals},
  author = {Erin Carmody and Victoria Gitman and Miha E. Habič},
  journal= {arXiv preprint arXiv:1609.07645},
  year   = {2021}
}

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23 pages