AXIOMATISABILITY OF WEAKLY FLAT, FLAT, AND PROJECTIVES-ACTS
Sydney Bulman‐Fleming, Victoria A. R. Gould · Communications in Algebra · 2002
This paper gives necessary and sufficient conditions on a monoid S that the class of flat left S-acts be (first order) axiomatisable. It presents also a streamlined version of the result of Stepanova that the class of projective left S-acts is axiomatisable if and only if the strongly flat left S-acts are axiomatisable and S is left perfect.