title: Prolog gives error "undefined procedure" when trying to use :-
body: <p>I'm using SWI-Prolog on Windows and am getting the following error:</p>
  
  <pre><code>14 ?- parent(X, Y) :- child(Y, X).
  ERROR: toplevel: Undefined procedure: (:-)/2 (DWIM could not correct)
  </code></pre>
  
  <p>I'm not entirely sure what's going on, as this worked last week and I am just starting to learn Prolog.</p>