1. Almeida, J.,Some order properties of the lattice of varieties of commutative semigroups, Canadian J. Math.38 (1986), 19?47.
2. Almeida, J.,The algebra of implicit operations, Algebra Universalis26 (1989), 16?32.
3. Almeida, J.,Residually finite congruences and quasi-regular subsets in uniform algebras, Portugali� Mathematica (to appear); a preliminary version (in Portuguese) appears in the proceedings of the second meeting of Portuguese algebraists, Porto 1987.
4. Agliano, P. andNation, J. B.,Lattices of pseudovarieties, manuscript, University of Hawaii, 1987.
5. Ash, C. J. Pseudovarieties, generalized varieties and similarly described classes, J. Algebra92 (1985), 104?115.