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Property $${(\hbar)}$$ and cellularity of complete Boolean algebras
Authors:Milo? S Kurili?  Stevo Todor?evi?
Institution:1.Department of Mathematics and Informatics,University of Novi Sad,Novi Sad,Serbia;2.U.F.R. de Mathématiques,Université Paris 7,Paris Cedex 05,France;3.Department of Mathematics,University of Toronto,Toronto,Canada
Abstract:A complete Boolean algebra \mathbbB{\mathbb{B}}satisfies property ((h/2p)){(\hbar)}iff each sequence x in \mathbbB{\mathbb{B}}has a subsequence y such that the equality lim sup z n = lim sup y n holds for each subsequence z of y. This property, providing an explicit definition of the a posteriori convergence in complete Boolean algebras with the sequential topology and a characterization of sequential compactness of such spaces, is closely related to the cellularity of Boolean algebras. Here we determine the position of property ((h/2p)){(\hbar)}with respect to the hierarchy of conditions of the form κ-cc. So, answering a question from Kurilić and Pavlović (Ann Pure Appl Logic 148(1–3):49–62, 2007), we show that ${``\mathfrak{h}{\rm -cc}\Rightarrow (\hbar)"}${``\mathfrak{h}{\rm -cc}\Rightarrow (\hbar)"}is not a theorem of ZFC and that there is no cardinal \mathfrakk{\mathfrak{k}}, definable in ZFC, such that ${``\mathfrak{k} {\rm -cc} \Leftrightarrow (\hbar)"}${``\mathfrak{k} {\rm -cc} \Leftrightarrow (\hbar)"}is a theorem of ZFC. Also, we show that the set { k: each k-cc c.B.a. has ((h/2p) ) }{\{ \kappa : {\rm each}\, \kappa{\rm -cc\, c.B.a.\, has}\, (\hbar ) \}}is equal to 0, \mathfrakh){0, \mathfrak{h})}or 0, \mathfrak h]{0, {\mathfrak h}]}and that both values are consistent, which, with the known equality {k: each c.B.a. having  ((h/2p) ) has the k-cc } = \mathfrak s, ¥){{\{\kappa : {\rm each\, c.B.a.\, having }\, (\hbar )\, {\rm has\, the}\, \kappa {\rm -cc } \} ={\mathfrak s}, \infty )}}completes the picture.
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