Abstract

In this paper we introduce the notion of a set algebra $\mathscr{S}$ satisfying a system $\mathscr{E}$ equations. After defining a notion of freeness for such algebras, we show that, for any system $\mathscr{E}$ of equations, set algebras that are free in the class of structures satisfying $\mathscr{E}$ exist and are unique up to a bisimulation. Along the way, analogues of classical set-theoretic and algebraic properties are investigated.