1. Yu. N. Kur'erov, "On solvability of one Ackermann class. Logic and mathematical foundations," in: Abstracts of papers at 8th All-Union Conf. on Logic and Methodology of Science [in Russian], Vil'nyus (1982), pp. 49?53.
2. Yu. N. Kur'erov, "On embedding of one Ackermann class in a graph grammer," Matem. Logika Ee Primen., No. 4, 89?99 (1985).
3. J. A. Robinson, "A machine-oriented logic based on the resolution principle," J. ACM,12, No. 1, 23?41 (1965).
4. Yu. N. Kur'erov, "On solvability by derivability of the ????*?* Ackermann class," in: Abstracts of papers at 8th All-Union Conf. on Mathematical Logic [in Russian], Nauka, Moscow (1986).
5. W. Ackermann, "Beitrage zum Entscheidungsproblem der mathematischen Logik," Mathem. Ann.,112, No. 3, 419?432 (1936).