1. A. Ja. Aĭzenštat, On varieties of semigroups having finite number of subvarieties, Algebraic Theory of Semigroups, Colloq. Math. Soc. János Bolyai, vol. 20, Amsterdam, New York, 1979, pp. 33-41.
2. Some order properties of the lattice of varieties of commutative semigroups;Almeida, Jorge;Canad. J. Math.,1986
3. Generalized varieties of commutative and nilpotent semigroups;Almeida, J.;Semigroup Forum,1984
4. Embedding the dual of 𝜋_{𝑚} in the lattice of equational classes of commutative semigroups;Burris, Stanley;Proc. Amer. Math. Soc.,1971
5. Totally commutative semigroups;Dudek, Józef;J. Austral. Math. Soc. Ser. A,1991