Semigroup quasivarieties: Two lattices and a reopened problem
Tim Koussas · International Journal of Algebra and Computation · 2021
We determine all quasivarieties of aperiodic semigroups that are contained in some residually finite variety. This endeavor was initially motivated by a problem in natural dualities, but our work here also serves as a partial correction to an error found in a result of Sapir from the 1980s.