# Wydawnictwa / Czasopisma IMPAN / Colloquium Mathematicum / Wszystkie zeszyty

## The spectrum of characters of ultrafilters on $\omega$

### Tom 111 / 2008

Colloquium Mathematicum 111 (2008), 213-220 MSC: Primary 03E05, 03E17. DOI: 10.4064/cm111-2-5

#### Streszczenie

We show the consistency of the statement: “the set of regular cardinals which are the characters of ultrafilters on $\omega$ is not convex”. We also deal with the set of $\pi$-characters of ultrafilters on $\omega$.

#### Autorzy

• Saharon ShelahThe Hebrew University of Jerusalem
Einstein Institute of Mathematics
Edmond J. Safra Campus, Givat Ram
Jerusalem 91904, Israel
and
Department of Mathematics
Hill Center, Busch Campus
Rutgers, The State University of New Jersey