 symmetrical in the two radii - which can be interchanged at
        will - in this case we need to make sure that <code class="computeroutput"><span class="identifier">a</span>
        <span class="special">&gt;=</span> <span class="identifier">b</span></code>
        so that we don't accidentally take the square root of a negative number:
      </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifi