title: List check that elements are different
body: <p>I would like to write a predicate different_from(Xs,X) which is a check that succeeds if and only if X is different from all the elements of the list Xs. </p>
  
  <p>So the query</p>
  
  <pre><code>different_from([3,2,5],4)
  </code></pre>
  
  <p>should succeed but this following query should fail:</p>
  
  <pre><code>different_from([3,2,5],2)
  </code></pre>
  
  <p>Since the predicate is a check it should not instantiate either of its arguments.</p>
  
  <p>thank you in advance for any help you can provide.</p>