nction</span></tt> must be Assignable, Copy Constructible, and
the expression <tt class="docutils literal"><span class="pre">f(*i)</span></tt> must be valid where <tt class="docutils literal"><span class="pre">f</span></tt> is a const object of
type <tt class="docutils literal"><span class="pre">UnaryFunction</span></tt>, <tt class="docutils literal"><span class="pre">i</span></tt> is an object of type <tt class="docutils literal"><span class="pre">Iterator</span></tt>, and
where the type of <tt class="docu