1. Orderings of ultrafilters;Blass;Ph. D. Thesis, Harvard University,1970
2. The intersection of non-standard models of arithmetic;Blass;J. Symb. Logic,1972
3. The Rudin-Keisler ordering on p-points;Blass;Trans. Amer. Math. Soc.,1973
4. Ultrafilter mappings and their Dedekind cuts;Blass;Trans. Amer. Math. Soc.,1974
5. Ultrafilters over a countable set;Booth;Ann. Math. Logic,1970