title: Where does the name "xs" for pattern matching come from?
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/6267735/what-is-the-history-of-the-variable-names-x-and-xs">What is the history of the variable names x and xs?</a>  </p>
  </blockquote>
  
  
  
  <p>Where does the canonical name "xs" in pattern matching come from? </p>
  
  <p>e.g. in </p>
  
  <pre><code>reverse' []     = []
  reverse' [x]    = [x]
  reverse' (x:xs) = reverse' xs ++ [x]  
  </code></pre>
  
  <p>Is it supposed to be the plural of "x" ?</p>