Club Stationary Reflection and other Combinatorial Principles at $\aleph_{\omega+2}$

TL;DR

This paper advances the understanding of combinatorial principles at the double successor of a countable cofinality singular cardinal, demonstrating models with the tree property, club stationary reflection, and approachability features.

Contribution

It introduces new models at _{+2} that satisfy complex combinatorial principles, including a novel indestructibility theorem for club stationary reflection.

Findings

Models with the tree property at _{+2}

Models with club stationary reflection at _{+2}

Preservation of club stationary reflection under certain forcing posets

Abstract

In this paper we continue the study in [Gilton-Levine-Stejskalova] of compactness and incompactness principles at double successors, focusing here on the case of double successors of singulars of countable cofinality. We obtain models which satisfy the tree property and club stationary reflection at these double successors. Moreover, we can additionally obtain either approachability or its failure. We also show how to obtain our results on $\aleph_{\omega+2}$ by incorporating collapses; particularly relevant for these circumstances is a new indestructibility theorem of ours showing that posets satisfying certain linked assumptions preserve club stationary reflection.