 The first step consist in looking at the formulas of any propositional language \(L\) as the terms of the algebraic first-order language with \(L\) as its set of operation symbols. This means that (i) every connective of \(L\) of arity \(n\) is taken as an operation symbol of arity \(n\) (thus every 0-ary symbol of \(L\) is taken as an individual constant) and that (ii) the propositional formulas of \(L\) are taken as the terms of this first-order language; in particular the propositional variables are the variables of the first-order language. From this point of view the definition of \(L\)-formula is exactly the definition of \(L\)-term. We will refer to the algebraic language with \(L\) as its set of operation symbols as the \(L\)-algebraic language.