Boolean-valued second-order logic revisited
Abstract
Following the paper~[3] by V\"{a}\"{a}n\"{a}nen and the author, we continue to investigate on the difference between Boolean-valued second-order logic and full second-order logic. We show that the compactness number of Boolean-valued second-order logic is equal to if there are proper class many Woodin cardinals. This contrasts the result by Magidor~[10] that the compactness number of full second-order logic is the least extendible cardinal. We also introduce the inner model constructed from Boolean-valued second-order logic using the construction of G\"{o}del's Constructible Universe L. We show that is the least inner model of closed under operators for all , and that enjoys various nice properties as G\"{o}del's L does, assuming that Projective Determinacy holds in any set generic extension. This contrasts the result by Myhill and Scott~[14] that the inner model constructed from full second-order logic is equal to HOD, the class of all hereditarily ordinal definable sets.
Keywords
Cite
@article{arxiv.2504.12602,
title = {Boolean-valued second-order logic revisited},
author = {Daisuke Ikegami},
journal= {arXiv preprint arXiv:2504.12602},
year = {2025}
}