Sh:1021

• Mildenberger, H., & Shelah, S. (2021). The cofinality of the symmetric group and the cofinality of ultrapowers. Israel J. Math., 242(1), 97–128. DOI: 10.1007/s11856-021-2124-2 MR: 4282078
• Abstract:
  We prove that {\mathfrak{{mcf}}} < {\rm cf} ({\rm{Sym}(\omega)}) and {\mathfrak{{mcf}}} > {\rm cf}({\rm{Sym}(\omega)})= {\mathfrak{{b}}} are both consistent relative to ZFC. This answers a question from [BanakhRepovsZdomskyy] and from [MdSh:967].
• Version 2019-02-21_11 (25p) published version (32p)

@article{Sh:1021,
 author = {Mildenberger, Heike and Shelah, Saharon},
 title = {{The cofinality of the symmetric group and the cofinality of ultrapowers}},
 journal = {Israel J. Math.},
 fjournal = {Israel Journal of Mathematics},
 volume = {242},
 number = {1},
 year = {2021},
 pages = {97--128},
 issn = {0021-2172},
 mrnumber = {4282078},
 mrclass = {03E35},
 doi = {10.1007/s11856-021-2124-2}
}