1. a) R.B. Woodward and R. Hoffmann, “The conservation of Orbital Symmetry”, Verlag Chemie, Academic Press, Weinheim 1970
2. b) Nguyen Trong Anh, “Les Regies de Woodward-Hoffmann”, Ediscience, Paris 1970
3. a) M.J.S. Dewar, “The MO Theory of Organic Chemistry”, McGraw-Hill, N.Y. 1969
4. b) M.J.S. Dewar and R.C. Dougherty, “The PMO Theory of Organic Chemistry”, Plenum Press, N.Y. 1975
5. c) H.E. Zimmerman, in “Pericyclic Reactions”, R.E. Lehr and A.P. Marchand Eds., Academic Press, N.Y. 1977, Vol. I, p. 53