1. Bukhstab A.A. Number theory. Ucpedgiz, 1960 (Russian).
2. Freivalds R. Fast computation by probabilistic Turing machines. — Ucenye Zapiski Latviiskogo Gosudarstvennogo Universiteta, v.233, 1975, 201–205 (Russian).
3. Freivalds R. Probabilistic machines can use less running time. — Information Processing '77, IFIP, North-Holland, 1977, 839–842.
4. Freivalds R. Capabilities of various models of probabilistic one-way automata. — Izvestiya VUZ. Matematika, No.5(228), 1981, 26–34 (Russian).
5. Freivalds R. Probabilistic two-way machines. — Lecture Notes in Computer Science, Springer, v.118, 1981, 33–45.