Totally commutative semigroups
Jo Dudek, Andrzej Kisielewicz · Journal of the Australian Mathematical Society Series A Pure Mathematics and Statistics · 1991
Abstract A semigroup is totally commutative if each of its essentially binary polynomials is commutative, or equivalently, if in every polynomial (word) every two essential variables commute. In the present paper we describe all varieties (equational classes) of totally commutative semigroups, lattices of subvarieties for any variety, and their free spectra.