Abstract
A monoid S 1 obtained by adjoining a unit element to a 2-testable semigroup S is said to be 2-testable. It is shown that a 2-testable monoid S 1 is either inherently non-finitely based or hereditarily finitely based, depending on whether or not the variety generated by the semigroup S contains the Brandt semigroup of order five. Consequently, it is decidable in quadratic time if a finite 2-testable monoid is finitely based.
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Lee, E.W.H. Finite basis problem for 2-testable monoids. centr.eur.j.math. 9, 1–22 (2011). https://doi.org/10.2478/s11533-010-0080-x
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DOI: https://doi.org/10.2478/s11533-010-0080-x