On characteristic properties of semigroups

Let $\mathcal{K}$ be a class of semigroups and $\mathcal{P}$ be a set of general properties of semigroups. We call a subset $Q$ of $\mathcal{P}$ characteristic for a semigroup $S\in\mathcal{K}$ if, up to isomorphism and anti-isomorphism, $S$ is the only semigroup in $\mathcal{K}$, which satisfies all the properties from $Q$. The set of properties $\mathcal{P}$ is called char-complete for $\mathcal{K}$ if for any $S\in \mathcal{K}$ the set of all properties $P\in\mathcal{P}$, 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 set for the class of semigroups of order $3$.