1. Hardy, G. H., D. E. Littlewood and G. Pólya: Inequalities (2nd edition). Cambridge 1952.
2. Hille, E., and R. S. Phillips groups (2nd edition). New York 1957.
3. Kendall, D. G.: Stochastic processes occurring in the theory of queues ... Ann math. Statistics 24, 338?354 (1953).
4. - Unitary dilations of Markov transition operators ... In U. Grenander (ed.), Probability and Statistics (Cramér memorial volume). Stockholm and New York 1959.
5. - Geometric ergodicity and the theory of queues. In K. J. Arrow, S. Karlin and P. Suppes (ed.), Mathematical methods in the social sciences. Stanford, California 1960.