1. Feller, W. 1968. “An introduction to probability theory and its applications, 3rd ed”. Vol. 1, New York: Wiley.
2. Feller, W. 1971. “An introduction to probability theory and its applications,2-nd ed”. Vol. 2, New York: Wiley.
3. Ross, S. M. 1983. “Stochastic processes”. New York: Wiley.