Congruence Preservation, Lattices and Recognizability

Abstract

We study in general algebras Gratzer's notion of congruence preserving function, characterizing functions in terms of stability under inverse image of particular Boolean algebras of subsets generated from any subset of the algebra. Weakening Gratzer's notion to only finite index congruences, a similar result holds with lattices of sets. Genereralizing the notion to that of stable preorder preserving function, we extend these characterizations to Boolean algebras and lattices generated from any recognizable subset of the algebra. Our starting point is a result with related flavor on the additive algebra of natural integers which was obtained some years ago. All these results can be visualized in the diagram of Table 1. We finally consider some simple particular conditions on the algebra allowing to get a richer diagram.