re>
<p>The function is parameterized on two property map types, <tt class="docutils literal"><span class="pre">AgeMap</span></tt> and
<tt class="docutils literal"><span class="pre">GPAMap</span></tt>, and takes a value parameter for each of those types.  The
function uses the <tt class="docutils literal"><span class="pre">property_traits</span></tt> interface to ascertain, at
compile-time, the value and key types of the property maps.  The code
then retrieves Fred's old information, using the <tt class="doc