A clone C is called equationally additive if the union of two C-algebraic
sets is again a C-algebraic set. We characterize the Mal?cev algebras whose
clone of polynomial functions is equationally additive in terms of properties
of the binary term condition commutator.
Joint work with E. Aichinger and M. Behrisch. Supported by the Austrian
Science Fund (FWF): P33878