English

On the consistency of ZF with an elementary embedding from $V_{\lambda+2}$ into $V_{\lambda+2}$

Logic 2024-03-19 v4

Abstract

According to a theorem due to Kenneth Kunen, under ZFC, there is no ordinal λ\lambda and non-trivial elementary embedding j:Vλ+2Vλ+2j:V_{\lambda+2}\to V_{\lambda+2}. His proof relied on the Axiom of Choice (AC), and no proof from ZF alone has been discovered. I0,λI_{0,\lambda} is the assertion, introduced by W. Hugh Woodin, that λ\lambda is an ordinal and there is an elementary embedding j:L(Vλ+1)L(Vλ+1)j:L(V_{\lambda+1})\to L(V_{\lambda+1}) with critical point <λ{<\lambda}. And I0I_0 asserts that I0,λI_{0,\lambda} holds for some λ\lambda. The axiom I0I_0 is one of the strongest large cardinals not known to be inconsistent with AC. It is usually studied assuming ZFC in the full universe VV (in which case λ\lambda must be a limit ordinal), but we assume only ZF. We prove, assuming ZF + I0,λI_{0,\lambda} + "λ\lambda is an even ordinal", that there is a proper class transitive inner model MM containing Vλ+1V_{\lambda+1} and satisfying ZF + I0,λI_{0,\lambda} + "there is an elementary embedding k:Vλ+2Vλ+2k:V_{\lambda+2}\to V_{\lambda+2}"; in fact we will have kjk\subseteq j, where jj witnesses I0,λI_{0,\lambda} in MM. This result was first proved by the author under the added assumption that Vλ+1#V_{\lambda+1}^\# exists; Gabe Goldberg noticed that this extra assumption was unnecessary. If also λ\lambda is a limit ordinal and λ\lambda-DC holds in VV, then the model MM will also satisfy λ\lambda-DC. We show that ZFC + "λ\lambda is even" + I0,λI_{0,\lambda} implies A#A^\# exists for every AVλ+1A\in V_{\lambda+1}, but if consistent, this theory does not imply Vλ+1#V_{\lambda+1}^\# exists.

Cite

@article{arxiv.2006.01077,
  title  = {On the consistency of ZF with an elementary embedding from $V_{\lambda+2}$ into $V_{\lambda+2}$},
  author = {Farmer Schlutzenberg},
  journal= {arXiv preprint arXiv:2006.01077},
  year   = {2024}
}

Comments

44 pages. Final author accepted version. For published version see https://doi.org/10.1142/S0219061324500132. Changes this version: reorganized order of presentation of some material (but no really new sections are present). Slightly generalized results by dealing with relevant triples (see Def 2.5, Theorem 4.2, etc). Various minor corrections and modifications

R2 v1 2026-06-23T15:58:05.271Z