title: Prolog apply predicate to list elements with maplist
body: <p>I am trying to do a simple tranformation to all elemnts of a list:</p>
  <pre><code> trans(X, M, Y):- Y is X*(-1) - M.
  </code></pre>
  <p>Then I am writing:</p>
  <p><code>maplist(trans, [1,2,3], NEW).</code>
  I am getting a just a <code>true</code> instead of a new list..</p>