1. G.Birkhoff, Universal Algebra,Proc. First Canadian Math. Congress, Montreal, University of Toronto Press, Toronto, 1946 (1945), 310–326.
2. G.Birkhoff, On groups of automorphisms (Spanish),Rev. Un. Mat. Argentina 11 (1946), 155–157.
3. S.Burris, On the structure of the lattice of equational classesL(T), Algebra Universalis 1 (1971), 39–45.
4. S.Burris and E.Nelson, Embedding the dual of II m in the lattice of equational classes of commutative semigroups},Proc. Amer. Math. Soc. 30 (1971), 37–39.
5. S.Burris and E.Nelson, Embedding the dual of II∞ in the lattice of equational classes of semigroups,Algebra Universalis 1 (1971), 248–253.