1. Adleman L.M. On distinguishing prime numbers from composite numbers. — Proc. 21st Symp. on Foundations of Computer Science, IEEE, 1980, 387–406.
2. Barzdin J.M. Complexity of recognition of palindromes by Turing machines. — Problemy kibernetiki, v.15, Moscow, Nauka, 1965, 245–248 (Russian).
3. Chandra A.K. and Stockmeyer L.J. Alternation. — Proc. 17th Symp. on Foundations of Computer Science, IEEE, 1976, 98–108.
4. Freivalds R. Fast computation by probabilistic Turing machines. — Učenye Zapiski Latviiiskogo Gosudarstvennogo Universiteta, v.233, 1975, 201–205. (Russian).
5. Freivalds R. Probabilistic machines can use less running time. Information Processing '77, IFIP, North-Holland, 1977, 839–842.