title: Check if all numbers in a list are different in prolog
body: <p>I want to create a rule in prolog that checks if there's a repeated number in a list.</p>
  
  <p>For example:</p>
  
  <ul>
  <li>for <code>[1,2,3,4]</code> it will return <code>true</code>. </li>
  <li>for <code>[1,2,3,3]</code> it will return <code>false</code> because the <code>3</code> is repeated</li>
  </ul>
  
  <p>I came up with this rule but it doesn't work</p>
  
  <pre><code>Different([]).
  Different([H|T]):-
       Member(H,T),
       Different(T).
  </code></pre>
  
  <p>Any ideas?</p>