On the extendability to Π30 ideals and Katětov order

Jialiang He, Jintao Luo, Shuguo Zhang

Research output: Contribution to journalArticlepeer-review


We show that there is a Σ40 ideal such that it’s neither extendable to any Π30 ideal nor above the ideal Fin×Fin in the sense of Katětov order, answering a question from M. Hrušák.

Original languageEnglish
JournalArchive for Mathematical Logic
StateAccepted/In press - 2024
Externally publishedYes

Bibliographical note

Publisher Copyright:
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.


  • Borel ideal
  • Ideal extendability
  • Katětov order
  • Primarily 54C65
  • Secondary 26A03, 03E17


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