title: projecting functional dependencies onto another relation
body: <p>consider the relation <code>R(ABCDE)</code> with the following FD's:</p>
  
  <ul>
  <li>AB -> C</li>
  <li>BC -> D</li>
  <li>CD -> E</li>
  <li>DE -> A</li>
  <li>AE -> B</li>
  </ul>
  
  <p>Project these FD's onto the relation of <code>S(ABCD)</code>. Which of the following FD's hold in the projected relation? </p>
  
  <ol>
  <li>A -> B</li>
  <li>A -> D</li>
  <li>BC -> A</li>
  <li>AC -> B</li>
  </ol>
  
  <p><em>the wording in the above question is directly copied from an assignment</em></p>
  
  <p>The correct answer is given to be 3.</p>
  
  <p>since the last 3 FD's contain E they do not hold in the projection onto R(ABCD) I believe. So that leaves me with
  <code>AB -&gt; C</code> and <code>BC -&gt; D</code> I can not figure out how to determine the correct answer from my current though process.</p>