English

Forcing axioms via ground model interpretations

Logic 2021-10-25 v1

Abstract

We study principles of the form: if a name σ\sigma is forced to have a certain property φ\varphi, then there is a ground model filter gg such that σg\sigma^g satisfies φ\varphi. We prove a general correspondence connecting these name principles to forcing axioms. Special cases of the main theorem are: Any forcing axiom can be expressed as a name principle. For instance, PFA\mathsf{PFA} is equivalent to a principle for rank 11 names (equivalently, nice names) for subsets of ω1\omega_1, and a principle for rank 22 names for sets of reals. Moreover, λ\lambda-bounded forcing axioms are equivalent to name principles. Bagaria's characterisation of BFA\mathsf{BFA} via generic absoluteness is a corollary. We further systematically study name principles where φ\varphi is a notion of largeness for subsets of ω1\omega_1 (such as being unbounded, stationary or in the club filter) and corresponding forcing axioms.

Keywords

Cite

@article{arxiv.2110.11781,
  title  = {Forcing axioms via ground model interpretations},
  author = {Philipp Schlicht and Christopher Turner},
  journal= {arXiv preprint arXiv:2110.11781},
  year   = {2021}
}
R2 v1 2026-06-24T07:06:21.793Z