1. Bühler, W. J.: Some results on the behaviour of branching processes. (Teor. Verojatn. Primen. 13, 51?62 (1968).
2. Feller, W.: An introduction to probability theory and its applications. Vol. II. New York: Wiley 1966.
3. Gnedenko, B. V.: Theory of probability. New York: Chelsea 1963.
4. Harris, T. E.:The theory of branching processes. Berlin-Göttingen-Heidelberg: Springer 1963.
5. Heathcote, C. R., E. Seneta, and D. Vere-Jones: A refinement of two theores in the theory of branching processes. Teor. Verojatn. Primen. 12, 341?346 (1967).