title: Prolog Error: Full stop in clause-body? Cannot redefine ,/2
body: <p>I just started learning prolog. I compiled a file with SWI-Prolog but got an error message: Prolog Error: Full stop in clause-body?   </p>
  
  <p>My file:</p>
  
  <pre><code>loves( vincent   , mia ) .
  loves( marsellus , mia ) .
  
  jealous(X,Y) :=
    loves(X,Z) ,
    loves(Y,Z) .
  </code></pre>