Finite Basis Problem for Semigroups of Order Five or Less: Generalization and Revisitation
Semigroup, Monoid, Finitely based, Hereditarily finitely based
A system of semigroup identities is hereditarily finitely based if it defines a variety all semigroups of which are finitely based. Two new types of hereditarily finitely based identity systems are presented. Two of these systems, together with eight existing systems, establish the hereditary finite basis property of every semigroup of order five or less with one possible exception.
Lee, Edmond W. H., "Finite Basis Problem for Semigroups of Order Five or Less: Generalization and Revisitation" (2013). Mathematics Faculty Articles. 10.