ss="special">=</span> <span class="keyword">false</span><span class="special">);</span>
   <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">Expression</span><span class="special">()</span><span class="keyword">const</span><span class="special">;</span>
   <span class="comment">//</span>
   <span class="comment">// now matching operators: </span>
   <span class="comment">// </span>
   <span class="keyword">bool</span> <span clas