Logical complexity of reducts of elementary algebraic classes
摘要
We examine how elementary classes of algebras can be represented as reducts of logically simpler classes. For example, we demonstrate that every elementary class is a reduct of a positive class, and that any variety is a reduct of a four-based variety. Additionally, we introduce hierarchies based on fragments of first-order logic to analyse these reducts, providing a more detailed structural understanding of the landscape of algebraic classes.