Some more axiomatisability for S-acts

This paper discusses necessary and sufficient conditions on a monoid S, such that the class of C-flat left $S$-acts is axiomatisable, where C is the class of all embeddings (of right ideals into S) of right S-acts. We consider the axiomatisability of some flatness classes of S-acts, which were previously discussed by Bulman-Fleming and Gould [1] . We present here a more general procedure to axiomatise these classes. A similar type of general results have been found for S-posets by Gould and Shaheen [10]. We have found that there are some classes of S-acts which are axiomatisable by more than one method. This has not been seen before.