title: Return a string
body: <p>Is it possible to return a string in <code>prolog</code>? It yes how may I do that?<br>
  I'll pass a name as parameter and I'd like to know what is the time that person is works, I tried this:<br>
  This returns me <code>true</code>.</p>
  
  <pre><code>work_at(sara) :- friday at 9.  
  time(X) :- work_at(X).
  </code></pre>
  
  <p>This gives me error.  </p>
  
  <pre><code>work_at(sara) :- "friday at 9".  
  time(X) :- work_at(X).  
  </code></pre>
  
  <p>If I want to know the time that someone works, like:  </p>
  
  <pre><code>time(sara).  
  </code></pre>
  
  <p>I'd like to know what day/time sara works.</p>