title: students whose majors are not listed?
body: <pre><code>&lt;univ&gt;
   &lt;student&gt;
   &lt;id&gt;1&lt;/id&gt;
   &lt;major&gt;cs&lt;/major&gt;
   &lt;/student&gt;
   &lt;student&gt;
   &lt;id&gt;2&lt;/id&gt;
   &lt;/student&gt;
    .... 
  &lt;/univ&gt;
  </code></pre>
  
  <p>How to find student ID's not having any major?
  So the output should be 2.</p>
  
  <p>Guess the one mentioned is wrong.
  /univ/student[not(major)]/id/text()</p>