# Sh:640

• Błaszczyk, A., & Shelah, S. (2001). Regular subalgebras of complete Boolean algebras. J. Symbolic Logic, 66(2), 792–800.
• 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.
• published version (10p)
Bib entry
@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}
}