English

A countable definable set of reals containing no definable elements

Logic 2018-09-05 v2

Abstract

We make use of a finite support product of Jensen forcing to define a model in which there is a countable non-empty lightface Π21\Pi^1_2 set of reals containing no ordinal-definable real.

Keywords

Cite

@article{arxiv.1408.3901,
  title  = {A countable definable set of reals containing no definable elements},
  author = {Vladimir Kanovei and Vassily Lyubetsky},
  journal= {arXiv preprint arXiv:1408.3901},
  year   = {2018}
}

Comments

Revised version. The revision includes an updated proof of Lemma 4.5 (the density-preservation lemma for the product)

R2 v1 2026-06-22T05:31:39.158Z