title: Pythonic way to create union of all values contained in multiple lists
body: <p>I have a list of lists:</p>
  
  <pre><code>lists = [[1,4,3,2,4], [4,5]]
  </code></pre>
  
  <p>I want to flatten this list and remove all duplicates; or, in other words, apply a set union operation:</p>
  
  <pre><code>desired_result = [1, 2, 3, 4, 5]
  </code></pre>
  
  <p>What's the easiest way to do this? </p>