r clear="all" style="clear: all;">

<hr>

<h2>Contents</h2>

<ul>
  <li><a href="#intro">Introduction</a>
    <ul>
      <li><a href="#read_write_key_extractors">Read/write key extractors</a></li>
    </ul>
  </li>
  <li><a href="#predefined_key_extractors">Predefined key extractors</a>
    <ul>
      <li><a href="#identity"><code>identity</code></a></li>
      <li><a href="#member"><code>member</code></a></li>
      <li><a href="#const_mem_fun"><code>const_mem_fun</code> and <code>mem_fun</code></a>
      