Inner models from extended logics and the Delta-operation
Abstract
If is an abstract logic (a.k.a. model theoretic logic), we can define the inner model by replacing first order logic with in G\"odel's definition of the inner model of constructible sets. Set theoretic properties of such inner models have been investigated recently and a spectrum of new inner models is emerging between and . The topic of this paper is the effect on of a slight modification of i.e. how sensitive is on the exact definition of ? The -extension of a logic is generally considered a "mild" extension of . We give examples of logics for which the inner model is consistently strictly smaller than the inner model , and in one case we show this follows from the existence of .
Keywords
Cite
@article{arxiv.2508.07892,
title = {Inner models from extended logics and the Delta-operation},
author = {Jouko Väänänen and Ur Ya'ar},
journal= {arXiv preprint arXiv:2508.07892},
year = {2026}
}
Comments
18 pages; minor revisions; accepted to Israel Journal of Mathematics