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Around ${\rm cofin}$

Volume 134 / 2014

Andrzej Rosłanowski, Saharon Shelah Colloquium Mathematicum 134 (2014), 211-225 MSC: Primary 03E17; Secondary 03E35. DOI: 10.4064/cm134-2-5


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)].


  • Andrzej RosłanowskiDepartment of Mathematics
    University of Nebraska at Omaha
    Omaha, NE 68182-0243, U.S.A.
  • Saharon ShelahInstitute of Mathematics
    The Hebrew University of Jerusalem
    91904 Jerusalem, Israel
    Department of Mathematics
    Rutgers University
    New Brunswick, NJ 08854, U.S.A.

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