mut Zeisel</dt>

      <dd>Contributed the 'left' operators and added some grouped operator
      classes.</dd>

      <dt>Daniel Frey</dt>

      <dd>Contributed the NRVO-friendly and symmetric implementation of
      arithmetic operators.</dd>

    </dl>

    <h2>Note for Users of <a name="old_lib_note">Older Versions</a></h2>

    <p>The <a href="#chaining">changes in the library interface and
    recommended usage</a> were motivated by some practical issues described
    below. The new version of the li