ass="code">nan</code> ('not a number')
   for <code class="code">0.0 /. 0.0</code>.  These special numbers then propagate through
   floating-point computations as expected: for instance,
   <code class="code">1.0 /. infinity</code> is <code class="code">0.0</code>, and any arithmetic operation with <code class="code">nan</code>
   as argument returns <code class="code">nan</code> as result.<br>

</p><pre><span id="VAL(~-.)"><span class="keyword">val</span> (~-.)</span> : <code class="type">float -&gt; floa