English

Inner models from extended logics and the Delta-operation

Logic 2026-03-04 v3

Abstract

If L\mathcal{L} is an abstract logic (a.k.a. model theoretic logic), we can define the inner model C(L)C(\mathcal{L}) by replacing first order logic with L\mathcal{L} in G\"odel's definition of the inner model LL of constructible sets. Set theoretic properties of such inner models C(L)C(\mathcal{L}) have been investigated recently and a spectrum of new inner models is emerging between LL and HOD\mathrm{HOD}. The topic of this paper is the effect on C(L)C(\mathcal{L}) of a slight modification of L\mathcal{L} i.e. how sensitive is C(L)C(\mathcal{L}) on the exact definition of L\mathcal{L}? The Δ\Delta-extension Δ(L)\Delta(\mathcal{L}) of a logic is generally considered a "mild" extension of L\mathcal{L}. We give examples of logics L\mathcal{L} for which the inner model C(L)C(\mathcal{L}) is consistently strictly smaller than the inner model C(Δ(L))C(\Delta(\mathcal{L})), and in one case we show this follows from the existence of 00^{\sharp}.

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

R2 v1 2026-07-01T04:44:08.315Z