On characteristic properties of semigroups

Abstract

Let K be a class of semigroups and P be a set of general properties of semigroups. We call a subset Q of P cha\-racteristic for a semigroup S∈ K if, up to isomorphism and anti-isomorphism, S is the only semigroup in K, which satisfies all the properties from Q. The set of properties P is called char-complete for K if for any S∈ K the set of all properties P∈ P, which hold for the semigroup S, is characteristic for S. We indicate a 7-element set of properties of semigroups which is a minimal char-complete setfor the class of semigroups of order 3.