1. 1. V. D. Belousov, Fundamentals of the Theory of Quasigroups and Loops [in Russian], Nauka, Moscow (1967).
2. 2. V. D. Belousov, "Systems of quasigroups with generalized identities," Uspekhi Mat. Nauk, 20, No. 1(121), 75-146 (1965)
3. English translation: Russ. Math. Surv., 20, No. 1, 75-143 (1965)
4. 3. V. D. Belousov, "Balanced identities in quasigroups," Math. Sb., 70(112), No. 1, 55-97 (1966) (in Russian).
5. 4. R. F. Koval', "Classification of quadratic functional equations of small length on quasigroups," Nauk. Chasopys Nats. Ped. Univ. Im. Dragomanova, Ser. Fiz.-Mat. Nauky, No. 5, 111-127 (2004) (in Ukrainian).