Equational characterization of the quaternary discriminator (Q1866800)

R. McKenzie gave an equational characterization of discriminator varieties in 1975. By a quaternary discriminator the author means a 4-ary function \(N\) such that \(N(a,b,c,d) = d\) for \(a\not = b\) and \(N(a,a,c,d) = c\). In a way similar to that of R. McKenzie, the author gives an equational characterization of varieties with a 4-ary term \(N\) each of whose directly decomposable members has this \(N\) as a quaternary discriminator.