Algebraic expansions of logics

Abstract

An algebraically expandable (AE) class is a class of algebraic structures axiomatizable by sentences of the form $\forall \exists!\wedge p=q$. For a logic $L$ algebraized by a quasivariety $\mathcal{Q}$ we show that the AEsubclasses of $\mathcal{Q}$ correspond to certain natural expansions of $L$, which we call algebraic expansions. These turn out to be a special case of the expansions by implicit connectives studied by $\mathbf{X}$. Caicedo. We proceed to characterize all the AE-subclasses of abelian $\ell$-groups and perfect MV-algebras, thus fully describing the algebraic expansions of their associated logics.