Uniform Birkhoff

Abstract

We show that pseudovarieties of finitely generated algebras, i.e., classes $C$ of finitely generated algebras closed under finite products, homomorphic images, and subalgebras, can be described via a uniform structure $U$ on the free algebra for $C$: the members of $C$ then are precisely those finitely generated algebras $A$ for which the natural mapping from the free algebra onto the term clone of $A$ is well-defined and uniformly continuous with respect to the uniformity $U$ and the uniformity of pointwise convergence on the term clone of $A$, respectively. Our result unifies earlier theorems describing pseudovarieties of finite algebras and the pseudovariety generated by a single oligomorphic algebra.

10 pages. (This material contains old results from 2014 published in 2018 (see reference), but so far not on arXiv)