 Consider a propositional language \(\mathcal{L}\) built upon a set of atomic sentences \(\mathcal{P}\) and a set of propositional connectives \(\mathcal{C}\) (the set of sentences of \(\mathcal{L}\) being the smallest set containing \(\mathcal{P}\) and being closed under the connectives from \(\mathcal{C})\). Then a valuation system \(\mathbf{V}\) for the language \(\mathcal{L}\) is a triple \(\langle \mathcal{V}, \mathcal{D}, \mathcal{F}\rangle\), where \(\mathcal{V}\) is a non-empty set with at least two elements, \(\mathcal{D}\) is a subset of \(\mathcal{V}\), and \(\mathcal{F} = \{f_{c _1},\ldots, f_{c _m}\}\) is a set of functions such that \(f_{c _i}\) is an \(n\)-place function on \(\mathcal{V}\) if \(c_i\) is an \(n\)-place connective. Intuitively, \(\mathcal{V}\) is the set of truth values, \(\mathcal{D}\) is the set of designated truth values, and \(\mathcal{F}\) is the set of truth-value functions interpreting the elements of \(\mathcal{C}\). If the set of truth values of a valuation system \(\mathbf{V}\) has \(n\) elements, \(\mathbf{V}\) is said to be \(n\)-valued. Any valuation system can be equipped with an assignment function which maps the set of atomic sentences into \(\mathcal{V}\). Each assignment \(a\) relative to a valuation system \(\mathbf{V}\) can be extended to all sentences of \(\mathcal{L}\) by means of a valuation function \(v_a\) defined in accordance with the following conditions: