Martin's Maximum and tower forcing
Abstract
There are several examples in the literature showing that compactness-like properties of a cardinal cause poor behavior of some generic ultrapowers which have critical point (Burke \cite{MR1472122} when is a supercompact cardinal; Foreman-Magidor \cite{MR1359154} when in the presence of strong forcing axioms). We prove more instances of this phenomenon. First, the Reflection Principle (RP) implies that if is a tower of ideals which concentrates on the class of -guessing, internally club sets, then is not presaturated (a set is -guessing iff its transitive collapse has the -approximation property as defined in Hamkins \cite{MR2540935}). This theorem, combined with work from \cite{VW_ISP}, shows that if or holds and there is an inaccessible cardinal, then there is a tower with critical point which is not presaturated; moreover this tower is significantly different from the non-presaturated tower already known (by Foreman-Magidor \cite{MR1359154}) to exist in all models of Martin's Maximum. The conjunction of the Strong Reflection Principle (SRP) and the Tree Property at has similar implications for towers of ideals which concentrate on the wider class of -guessing, internally stationary sets. Finally, we show that the word "presaturated" cannot be replaced by "precipitous" in the theorems above: Martin's Maximum (which implies SRP and the Tree Property at ) is consistent with a precipitous tower on .
Keywords
Cite
@article{arxiv.1110.1584,
title = {Martin's Maximum and tower forcing},
author = {Sean Cox and Matteo Viale},
journal= {arXiv preprint arXiv:1110.1584},
year = {2011}
}