Blowing up and blurring finite Monk and rainbow algebras

Abstract

We use Monk like algebras to give a new proof that the classes of strongly representable relation algebras and finite dimensional cylindric algebras of dimension >2 are not elementary. Our construction is based on relation algebras have cylindric basis, so that we obtain the result for both in one go, since they are both based on the same graph. The proof also uses Erdos' graphs. We also show using a rainbow construction that the class SNr_n\CA_{n+k} is not atom canonical, for any k\geq 4.