1. V. N. Red'ko, ?Definor algebras and algebras of languages,? Kibernetika, No. 4 (1973).
2. L. P. Lisovik, ?Generalized finite generators and the identity problem for definor algebras of regular events,? Kibernetika, No. 1 (1975).
3. V. N. Red'ko, ?On the algebra of commutative evens,? Ukrainsk, Mat. Zh.,16, No. 2 (1964).
4. M. A. Taitslin, ?On elementary theories of commutative semigroup,? in: Algebra and Logic [in Russian], Vol. 5, No. 4, Novosibirsk (1966).
5. V. N. Redko, ?Pro Komutativne Zamikaniya Podii,? [in Ukrainian], Dopovidi Akad. Nauk UKrSSR, No. 9, Kiev (1963).