1. Whittaker and WatsonModern Analysis, p. 412.
2. N. F. Mott and H. JonesThe theory of the properties of the metals and alloys, 1936.
3. E. Wigner, L. P. Bouckaert and R. Smoluchowski,Physical Review, 1936,50, 58.
4. S. Bhagavantam and T. VenkatarayuduTheory of groups and its application to physical problems, Andhra University Publications, 1948.