When does every definable nonempty set have a definable element?
Logic
2017-06-23 v1
Abstract
The assertion that every definable set has a definable element is equivalent over ZF to the principle , and indeed, we prove, so is the assertion merely that every -definable set has an ordinal-definable element. Meanwhile, every model of ZFC has a forcing extension satisfying in which every -definable set has an ordinal-definable element. Similar results hold for and and other natural instances of .
Keywords
Cite
@article{arxiv.1706.07285,
title = {When does every definable nonempty set have a definable element?},
author = {François G. Dorais and Joel David Hamkins},
journal= {arXiv preprint arXiv:1706.07285},
year = {2017}
}
Comments
9 pages. Commentary concerning this article can be made at http://jdh.hamkins.org/definable-sets-with-definable-elements