1. Chung, K. L.: Markov chains with stationary transition probabilities. Berlin-Göttingen-Heidelberg: Springer-Verlag 1960.
2. Doob, J. L.: Stochastic processes. New York: J. Wiley & Sons, Inc. 1953.
3. Feller, W.: An introduction to probability theory and its applications. 2. Aufl. New York: J. Wiley & Sons, Inc. 1958
4. Bellman, R., andR. Kalaba: Random walk, scattering and invariant imbedding. Proc. Nat. Acad. Sci. U. S.43, 930?933 (1957).
5. Bellman, R., andR. Kalaba: Invariant imbedding, random walk and scattering. II. Discrete versions. J. Math. Mech.9, 411?419 (1960).