1. Athreya, K. B. and Ney, P. E. (1972). Branching Processes. Springer, Berlin.
2. Bruijn, N. G. de (1959). Nieuw Arch. Wisk. 7, 20–26.
3. Feller, W. (1971). An Introduction to Probability Theory and Its Applications, Vol. 2, Wiley, New York. ( 2nd edn. )
4. Seneta, E. (1968). Ann. Math. Statist. 39, 2098–2102.
5. Seneta, E. (1974a). Adv. Appl. Prob. 6, 408–420.