On the lattice of sub-pseudovarieties of DA

Abstract

The wealth of information that is available on the lattice of varieties of bands, is used to illuminate the structure of the lattice of sub-pseudovarieties of DA, a natural generalization of bands which plays an important role in language theory and in logic. The main result describes a hierarchy of decidable sub-pseudovarieties of DA in terms of iterated Mal'cev products with the pseudovarieties of definite and reverse definite semigroups.