"><span class="pre">r</span></tt> is past-the-end</td>
</tr>
<tr><td><tt class="literal"><span class="pre">a</span> <span class="pre">==</span> <span class="pre">b</span></tt></td>
<td>convertible to <tt class="literal"><span class="pre">bool</span></tt></td>
<td><tt class="literal"><span class="pre">==</span></tt> is an equivalence
relation over its domain</td>
</tr>
<tr><td><tt class="literal"><span class="pre">a</span> <span class="pre">!=</span> <span class="pre">b</span></tt></td>
<td>convertible to <t