title: SWI Prolog vs. GNU Prolog - CLP(FD) issues under SWI
body: <p>I wrote a quick predicate in Prolog trying out CLP(FD) and its ability to solve systems of equations.</p>
  
  <pre><code>problem(A, B) :-
      A-B #= 320,
      A #= 21*B.
  </code></pre>
  
  <p>When I call it in SWI, I get:</p>
  
  <pre><code>?- problem(A,B).
  320+B#=A,
  21*B#=A.
  </code></pre>
  
  <p>Whereas in GNU, I get the correct answer of:</p>
  
  <pre><code>| ?- problem(A,B).
  
  A = 336
  B = 16
  </code></pre>
  
  <p>What's going on here? Ideally I'd like to get the correct results in SWI as it's a much more robust environment.</p>