The spectrum of characters of ultrafilters on omega [article]

Saharon Shelah
2007 arXiv   pre-print
We show the consistency of the set of regular cardinals which are the character of some ultrafilter on omega is not convex. We also deal with the set of pi chi-characters of ultrafilters on omega.
arXiv:math/0612240v2 fatcat:5onlferq7rg33chfilqq4ydmlm