1. Ultrafilters on a Countable Set;Booth;Ann. of Math. Logic,1970
2. Ketonen, K., 1971, Ultrafilters and Independent Sets
3. A General Theory of Monads;Luxemburg,1969
4. Lectures on Non-Standard Analysis;Machover,1969
5. Puritz, C., 1972, Skies, Constellations and Monads, this volume