al floating-point value denoting the result of an
    undefined operation such as <code class="code">0.0&nbsp;/.&nbsp;0.0</code>.  Stands for
    'not a number'.  Any floating-point operation with <code class="code">nan</code> as
    argument returns <code class="code">nan</code> as result.  As for floating-point comparisons,
    <code class="code">=</code>, <code class="code">&lt;</code>, <code class="code">&lt;=</code>, <code class="code">&gt;</code> and <code class="code">&gt;=</code> return <code class=