title: Comparing prolog anonymous variables
body: <p>I have a series of facts in prolog that contain the anonymous variable <code>_</code>.</p>
  
  <pre><code>fact(a, _).
  fact(b, _).
  fact(c, _).
  </code></pre>
  
  <p>and i have some rules that take in lists of these facts:</p>
  
  <pre><code>f([H | T]) :- H == fact(a, _),
                % stuff %
                .
  </code></pre>
  
  <p>however this is not working. The rule is not going past the first clause <code>H == fact(a, _)</code>. What am I doing wrong? Is there a different operator for equality?</p>