1. Birkhoff, G. On the structure of abstract algebras.Proceedings of the Cambridge Philosophical Society, 1935,31, 433–54.
2. Birkhoff, G.Lattice theory. Providence, Rhode Island: American Mathematical Society, 1967.
3. Green, P. E. and Carmone, F. J.Multidimensional scaling and related techniques in marketing analysis. Boston: Allyn and Bacon, 1970.
4. Jakobson, R., and Halle, M.Fundamentals of language. The Hague: Mouton, 1965.
5. Johnson, S. C. Hierarchical clustering schemes.Psychometrika, 1967,32, 241–254.