1. Balaban, A. T., Farcasiu, D., Banica, R.: Rev. Roum. Chim. 11, 1205 (1966).
2. For a concise explanation of graph theoretical terms see: Essam, J. W., Fisher, M. E.: Rev. Mod. Phys., 42, 272 (1970)
3. For an introduction to graph theoretical concepts see: Wilson, R. J.: Introduction to Graph Theory, London: Longman, 1972
4. Harary, F.: Graph Theory, p. 165. Reading, Mass.: Addison-Wesley, 1969
5. Balaban, A. T.: Rev. Roum. Chim. 18, 811 (1973)