> <code class="literal">+</code> <code class="type">anyrange</code>
        → <code class="returnvalue">anyrange</code>
       </p>
       <p>
        Computes the union of the ranges.  The ranges must overlap or be
        adjacent, so that the union is a single range (but
        see <code class="function">range_merge()</code>).
       </p>
       <p>
        <code class="literal">numrange(5,15) + numrange(10,20)</code>
        → <code class="returnvalue">[5,20)</code>
       </p></td></tr><tr><td cla