Sh:640

• Błaszczyk, A., & Shelah, S. (2001). Regular subalgebras of complete Boolean algebras. J. Symbolic Logic, 66(2), 792–800. arXiv: math/9712285 DOI: 10.2307/2695044 MR: 1833478
• Abstract:
  It is shown that there exists a complete, atomless, \sigma-centered Boolean algebra, which does not contain any regular countable subalgebra if and only if there exist a nowhere dense ultrafilter. Therefore the existence of such algebras is undecidable in ZFC.
• Version 1999-11-27_10 (12p) published version (10p)

@article{Sh:640,
 author = {B{\l}aszczyk, Aleksander and Shelah, Saharon},
 title = {{Regular subalgebras of complete Boolean algebras}},
 journal = {J. Symbolic Logic},
 fjournal = {The Journal of Symbolic Logic},
 volume = {66},
 number = {2},
 year = {2001},
 pages = {792--800},
 issn = {0022-4812},
 mrnumber = {1833478},
 mrclass = {03E40 (03G05 06E05)},
 doi = {10.2307/2695044},
 note = {\href{https://arxiv.org/abs/math/9712285}{arXiv: math/9712285}},
 arxiv_number = {math/9712285}
}