title: Check if item is in a list (Lisp)
body: <p>What's a simple way to check if an item is in a list?</p>
  
  <p>Something like</p>
  
  <pre><code>(in item list)
  </code></pre>
  
  <p>might return <code>true</code> if <code>item=1</code> and <code>list=(5 9 1 2)</code> and <code>false</code> if <code>item=7</code></p>