=====Congruence e-regularity=====

An algebra with a constant term $e$ is \emph{congruence $e$-regular} if each congruence relation of the algebra is
determined by its $e$-congruence class, i.e., for all congruences $\theta$, $\psi$ of the algebra
$[e]_{\theta}=[e]_{\psi}\Longrightarrow
\theta =\psi$.

A class of algebras is \emph{congruence $e$-regular} if each of its members is congruence $e$-regular for a fixed constant term $e$ in
the language of the class. 

Congruence $e$-regularity holds for many 'classical' varieties such as groups, rings and vector spaces. 

This property can be characterized by a Mal'cev condition ...