title: Library function to find difference between two lists - OCaml
body: <p>Is there a library function to find <code>List1 minus elements that appear in List2</code>?  I've been googling around and haven't found much. </p>
  
  <p>It doesn't seem <em>too</em> trivial to write it myself. I've written a function to remove a specific element from a list but that's much more simple:</p>
  
  <pre><code>let rec difference l arg = match l with
  | [] -&gt; []
  | x :: xs -&gt; 
      if (x = arg) then difference xs arg
      else x :: difference xs arg;;
  </code></pre>