title: C# Combine Two Lists With Overlapping Data
body: <p>If I have 2 lists of strings</p>
  
  <pre><code>List&lt;string&gt; history = new List&lt;string&gt;(){ "AA", "BB", "CC", "AA" };
  List&lt;string&gt; potentialNew = new List&lt;string&gt;(){ "CC", "AA", "DD", "EE", "FF", "AA"};
  </code></pre>
  
  <p>I need a way to combine the lists while preventing "overlap" and retaining the same ordering. So, in the example above, there would be a combined list that is:</p>
  
  <pre><code>AA, BB, CC, AA, DD, EE, FF, AA
  </code></pre>
  
  <p>In other words only <strong>DD, EE, FF, and AA</strong> are added to the <code>history</code> list. </p>
  
  <p>I've been trying to figure this out for a few days now, and countless searches have yielded no solution. Any help would be greatly appreciated!</p>