Abstract
This cardinal function is rather easy to describe, at least if we do not try to go into the detail that we did for cellularity, for example. If A is a subalgebra or homomorphic image of B, then |UltA| ≤ |UltB|. For weak products we have |∏ i∈Iw A i |= max(ω, sup i ∈I |UltA i |). The situation for full products is more complicated:
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© 1996 Springer Basel AG
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Monk, J.D. (1996). Number of ultrafilters. In: Cardinal Invariants on Boolean Algebras. Progress in Mathematics. Birkhäuser, Basel. https://doi.org/10.1007/978-3-0346-0334-8_20
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DOI: https://doi.org/10.1007/978-3-0346-0334-8_20
Publisher Name: Birkhäuser, Basel
Print ISBN: 978-3-0346-0333-1
Online ISBN: 978-3-0346-0334-8
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