1. Aho, A., Ullman, J.D.: The theory of parsing, translation and compiling, vol 1. Englewood Cliffs, NJ: Prentice Hall 1972
2. Paun, Gh., Salomaa, A.: Semi-commutativity sets ? a cryptographically grounded topic. Bull. Math. Soc. Sci. Math. Roumanie35, 3?4 (1991)
3. Rayward-Smith, V.J.: Mealy machines as coding devices. In: Beker, H.J., Poper, F.C. (eds.) Cryptography and codings. Oxford: Clarendon Press 1989
4. Salomaa, A.: Public-key cryptography. Berlin Heidelberg New York: Springer 1990
5. Salomaa, A., Sàntean Lila: Secret selling of secrets with several buyers. Bull EATCS42, 178?186 (1990)