1. F. Harary, in:Beitrage zur Graphentheorie (Teubner, Leipzig, 1968), pp. 49–60.
2. F. Harary,Graph Theory (Addison-Wesley, Reading, MA, 1969).
3. S.J. Cyvin and I. Gutman,Kekulé Structures in Benzenoid Hydrocarbons (Springer, Berlin, 1988).
4. Advances in the Theory of Benzenoid Hydrocarbors, ed. I. Gutman and S.J. Cyvin (Springer, Berlin, 1990).
5. J.R. Dias,Handbook of Polycyclic Hydrocarbons. Part A: Benzenoids (Elsevier, Amsterdam, 1988); I, Gutman and S.J. Cyvin,Introduction to the Theory of Benzenoid Hydrocarbons (Springer, Berlin, 1989).