><span class="identifier">factor</span></code>. Now, the
      production rule <code class="computeroutput"><span class="identifier">expression</span></code>
      in our grammar specification, traditionally called the <code class="computeroutput"><span class="identifier">start</span></code>
      symbol, can recognize inputs such as:
    </p>
<pre class="programlisting"><span class="number">12345</span>
<span class="special">-</span><span class="number">12345</span>
<span class="special">+</span><span clas