Cofinalities of Borel ideals

0430394 - MÚ 2015 RIV DE eng J - Článek v odborném periodiku
Hrušák, M. - Rojas-Rebolledo, D. - Zapletal, Jindřich
Cofinalities of Borel ideals.
Mathematical Logic Quarterly. Roč. 60, 1-2 (2014), s. 31-39. ISSN 0942-5616. E-ISSN 1521-3870
Grant CEP: GA AV ČR IAA100190902
Institucionální podpora: RVO:67985840
Klíčová slova: Borel ideals * natural numbers
Kód oboru RIV: BA - Obecná matematika
Impakt faktor: 0.325, rok: 2014
http://onlinelibrary.wiley.com/doi/10.1002/malq.201200079/abstract

We study the possible values of the cofinality invariant for various Borel ideals on the natural numbers. We introduce the notions of a fragmented and gradually fragmented F sigma ideal and prove a dichotomy for fragmented ideals. We show that every gradually fragmented ideal has cofinality consistently strictly smaller than the cardinal invariant b and produce a model where there are uncountably many pairwise distinct cofinalities of gradually fragmented ideals.
Trvalý link: http://hdl.handle.net/11104/0235339