Comfort, W. W. Ultrafilters: Some old and some new results. (English) Zbl 0355.54005 Bull. Am. Math. Soc. 83, 417-455 (1977). MSC: 54A25 03E05 11P81 54C45 54G10 PDFBibTeX XMLCite \textit{W. W. Comfort}, Bull. Am. Math. Soc. 83, 417--455 (1977; Zbl 0355.54005) Full Text: DOI
Neumann, P. M. The inequality of SQPS and QSP as operators on classes of groups. (English) Zbl 0209.32102 Bull. Am. Math. Soc. 76, 1067-1069 (1970). MSC: 20A05 PDFBibTeX XMLCite \textit{P. M. Neumann}, Bull. Am. Math. Soc. 76, 1067--1069 (1970; Zbl 0209.32102) Full Text: DOI
Bernstein, B. A. Operations with respect to which the elements of a Boolean algebra form a group. (English) JFM 49.0032.05 Bull. Am. Math. Soc. 29, 436 (1923). MSC: 20A05 PDFBibTeX XMLCite \textit{B. A. Bernstein}, Bull. Am. Math. Soc. 29, 436 (1923; JFM 49.0032.05)