Around ${\rm cofin}$
Volume 134 / 2014
Colloquium Mathematicum 134 (2014), 211-225
MSC: Primary 03E17; Secondary 03E35.
DOI: 10.4064/cm134-2-5
Abstract
We show the consistency of “there is a nice $\sigma $-ideal ${\mathcal I}$ on the reals with ${\rm add}({\mathcal I})=\aleph _1$ which cannot be represented as the union of a strictly increasing sequence of length $\omega _1$ of $\sigma $-subideals”. This answers [Borodulin-Nadzieja and Głąb, Math. Logic Quart. 57 (2011), 582–590, Problem 6.2(ii)].
