title: Find the Keys in a Prolog Pairs List
body: <p>I currently have a list of (Key,Value) pairs and I want to pull out all the keys to use in another function. </p>
  
  <p>Such that I have a list called </p>
  
  <pre><code>PairsList 
  </code></pre>
  
  <p>and I want to </p>
  
  <pre><code>retractall(map(Key,_).
  </code></pre>
  
  <p>I have tried:</p>
  
  <pre><code>retractall(map(PairsList[(Key,_)],_).
  </code></pre>
  
  <p>but that just throws a syntax error.</p>
  
  <p>Any help would be super! </p>