Type: Article
Publication Date: 1991-05-01
Citations: 19
DOI: https://doi.org/10.2140/pjm.1991.149.13
Our main result is that the proper forcing axiom (PFA) is equiconsistent with "PFA + there is a nonreflecting stationary subset of a>2."More generally we show for any cardinals n < m < N2 that if PFA + (n) is consistent with ZFC then so is "PFA + («) + there are m mutually nonreflecting stationary subsets of ω 2 ."As corollaries we can show that if n < m < Ni then PFA + («) (if consistent) does not imply PFA + (m), and that PFA (if consistent) does not imply Martin Vs maximum.