title: Removing common elements in two lists
body: <p>I have two sorted lists of positive integers which can have repeated elements and I must remove matching pairs of numbers, one from each list:</p>
  
  <pre><code>a=[1,2,2,2,3]
  b=[2,3,4,5,5]
  </code></pre>
  
  <p>should become:</p>
  
  <pre><code>a=[1,2,2]
  b=[4,5,5]
  </code></pre>
  
  <p>That is, the 2's and the 3's have been removed because they appear in both lists.</p>
  
  <p>Set intersection can't be used here because of the repeated elements.</p>
  
  <p>How do I go about this?</p>