Geodesic
The spectrum of characters of ultrafilters on $\omega$
Saharon Shelah1
1 The 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 110 Frelinghuysen Road Piscataway, NJ 08854-8019, U.S.A.
Colloquium Mathematicum, Tome 111 (2008) no. 2, pp. 213-220.

Voir la notice de l'article provenant de la source Institute of Mathematics Polish Academy of Sciences

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 $.
DOI : 10.4064/cm111-2-5
Keywords: consistency statement set regular cardinals which characters ultrafilters omega convex set characters ultrafilters omega

Saharon Shelah 1

1 The 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 110 Frelinghuysen Road Piscataway, NJ 08854-8019, U.S.A. 
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Saharon Shelah. The spectrum of characters of ultrafilters on 
$\omega$. Colloquium Mathematicum, Tome 111 (2008) no. 2, pp. 213-220. doi : 10.4064/cm111-2-5. http://geodesic.mathdoc.fr/articles/10.4064/cm111-2-5/

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