1. A. Ramakrishnan, Handbuch der Physik III/2, 413 (Springer-Verlag, 1959).
2. M.S. Bartlett, “An introduction to stochastic processes” Cambridge University Press, (1955).
3. A. Papoulis, “Probability, random variables and stochastic processes” McGraw Hill, New York.
4. Yu.A. Prophorov and Yu.A. Rozanov, “Probability Theory” Springer-Verlag (1969).
5. E. Lukas, “Characteristic functions”, Griffin Monographs No.5, London (1960).