1. Kier, L. B., Hall, L. H.: Molecular connectivity in chemistry and drug research. New York: Academic Press 1976
2. Balaban, A. T., (Ed.): Chemical applications of graph theory. New York: Academic Press 1976
3. Hosoya, H., Hosoi, K.: J. Chem. Phys. 64, 1065 (1976); Hosoya, H., Hosoi, K., Gutman, I.: Theoret. Chim. Acta (Bed.) 38, 37 (1975); Hosoya, H., Murakami, M.: Bull. Chem. Soc. Japan 48, 3512 (1975); Hosoya, H.: Bull. Chem. Soc. Japan 44, 2332 (1971)
4. Simmons, H. E., Merrifield, R. E.: Proc. Natl. Acad. Sci. 74, 2616 (1977)
5. Two texts which we have found particularly useful are: Munkries, J. R.: Topology: A first course. Englewood Cliffs, N.J.: Prentice-Hall 1975; Dugundji, J.: Topology. Boston: Allyn and Bacon 1966