title: What does the logic operator "not" mean in EL
body: <p>Given the following code:</p>
  
  <pre><code>&lt;%
  java.util.Map map = new java.util.HashMap();
  request.setAttribute("map", map);
  map.put("a", "true");
  map.put("b", "false");
  map.put("c", "42"); 
  %&gt;
  
  ${not map.c}
  </code></pre>
  
  <p>the output of <code>${not map.c}</code> is true.... what kind of operation is this expression? and why the result from it is true?</p>