de> excludes the special
   <code class="type">timestamp</code> value <code class="literal">infinity</code>,
   while <code class="literal">[today,infinity]</code> include it, as does
   <code class="literal">[today,)</code> and <code class="literal">[today,]</code>.
  </p><p>
   The functions <code class="literal">lower_inf</code>
   and <code class="literal">upper_inf</code> test for infinite lower
   and upper bounds of a range, respectively.
  </p></div><div class="sect2" id="RANGETYPES-IO"><div class="