 If \(\phi\) is an \(\mathbf{IFL}\) formula, generated by the above clauses from some \(\mathbf{FO}\) formula \(\phi^*\), the free variables of \(\phi\) are simply the free variables of \(\phi^*\). \(\mathbf{IFL}\) formulas without free variables are \(\mathbf{IFL}\)  sentences.[18]