1. V. M. Glushkov, ?Abstract theory of automata,? Usp. Mat. Nauk,16, No. 5 (1961).
2. V. M. Glushkov and A. A. Letichevskii, ?Theory of discrete transducers?, in: Selected Aspects of Algebra and Logic [in Russian], Sib. Otd., Nauka, Novosibirsk (1971).
3. A. A. Letichevskii, ?Functional equivalence of discrete transducers. I,? Kibernetika, No. 2 (1969).
4. A. A. Letichevskii, ?Equivalence of automata with final state. I,? Kibernetika, No. 4 (1966).
5. A. A. Letichevskii, ?Equivalence of automata with final state. II,? Kibernetika, No. 1 (1967).