English

Ordinal definability in $L[\mathbb{E}]$

Logic 2026-04-15 v2

Abstract

Let MM be a tame mouse modelling ZFC. We show that MM satisfies "V=HODxV=\mathrm{HOD}_x for some real xx", and that the restriction E[ω1M,ORM)\mathbb{E}\upharpoonright[\omega_1^M,\mathrm{OR}^M) of the extender sequence EM\mathbb{E}^M of MM to indices above ω1M\omega_1^M is definable without parameters over the universe of MM. We show that MM has universe HODM[X]\mathrm{HOD}^M[X], where X=Mω1MX=M|\omega_1^M is the initial segment of MM of height ω1M\omega_1^M (including EMω1M\mathbb{E}^M\upharpoonright\omega_1^M), and that HODM\mathrm{HOD}^M is the universe of a premouse over some tω2Mt\subseteq\omega_2^M. We also show that MM has no proper grounds via strategically σ\sigma-closed forcings. We then extend some of these results partially to non-tame mice, including a proof that many natural φ\varphi-minimal mice model "V=HODV=\mathrm{HOD}", assuming a certain fine structural hypothesis whose proof has almost been given elsewhere.

Cite

@article{arxiv.2012.07185,
  title  = {Ordinal definability in $L[\mathbb{E}]$},
  author = {Farmer Schlutzenberg},
  journal= {arXiv preprint arXiv:2012.07185},
  year   = {2026}
}

Comments

48 pages. Added hypotheses to Thms 1.4 and 1.6, to bridge minor gaps in their former "proofs". Appeal to [6, Thm 0.2] (in paper's references) for Thm 4.2 clarified. Last part of proof of Thm 4.7 clarified. Added Lem 8.14 and strengthened Lem 8.13, to establish what was claimed to be an "immediate consequence" of STH in previous version. Other minor corrections and improvements in exposition

R2 v1 2026-06-23T20:56:15.594Z