1. Aı̌zenštat, A.Ya.: On some sublattices of the lattice of semigroup varieties. In: Modern Algebra, vol. 1, pp. 3–15. Leningrad State Pedagogical Institute, Leningrad (1974) [Russian]
2. Burris, S., Nelson, E.: Embedding the dual of Π m in the lattice of equational classes of commutative semigroups. Proc. Am. Math. Soc. 30, 37–39 (1971)
3. Burris, S., Nelson, E.: Embedding the dual of Π∞ in the lattice of equational classes of semigroups. Algebra Univers. 1, 248–254 (1971)
4. Evans, T.: The lattice of semigroup varieties. Semigroup Forum 2, 1–43 (1971)
5. Grätzer, G.: General Lattice Theory, 2nd edn. Birkhäuser, Basel (1998)