1. Effective coloration;Bean;J. Symbolic Logic,1976
2. Orderings of Ultrafilters;Blass,1970
3. A colour problem for infinite graphs and a problem in the theory of relations;de Bruijn;Proc. Sect. Sci., Ser. A: Math. Sci.,1951
4. Ultrafilters and ultraproducts in non-standard analysis;Cherlin,1972
5. The Theory of Ultrafilters;Comfort,1974