 A way to introduce algebras is as the models of some algebraic first-order language. We follow an equivalent route and give the definition of algebra using the setting of propositional languages. Let \(L\) be a propositional language. An algebra \(\bA\) of type \(L\), or \(L\)-algebra for short, is a set \(A\), called the carrier or the universe of \(\bA\), together with a function \(* ^{\bA}\) on \(A\) of the arity of \(*\), for every connective \(*\) in \(L\) (if \(*\) is 0-ary, \(* ^{\bA}\) is an element of \(A)\). An algebra \(\bA\) is trivial if its carrier is a one element set.