n{ConA\

We started this chapter looking at products as a way to produce larger and more complicated algebras out of given algebras. But we have also looked at this process in the other direction: we can try to express any algebra as a product of certain "simpler" algebras, such as irreducible algebras. However, direct products are not the best concept to use here, since not every algebra is isomorphic to a direct product of directly irreducible algebras. Subdirect products, on the other hand, do have the right property, as shown by the following theorem of G. Birkhoff ([8]). We present this important result without proof.