class="parameter"><code>n</code></em> be less than <em class="parameter"><code>f</code></em>.
            Reverse mappings such as
            <math overflow="scroll">

                <mrow>
                    <mi mathvariant="italic">n</mi>
                    <mo>=</mo>
                    <mn>1</mn>
                </mrow>
            </math>,
            and
            <math overflow="scroll">

                <mrow>
                    <mi mathvariant="italic">f</mi>
                    <mo>=</mo>
 