title: Easy way to compare two List<String> and keep only unique values
body: <p>I am trying to Compare two lists and keep on each list only items that are unique to each list. Could you assist? </p>
  
  <p>I know how to do intersection, but I actually need to do the opposite</p>
  
  <pre><code>        //Example
          List&lt;String&gt; baseListCopy = new List&lt;String&gt;();
          baseListCopy.Add("Test1");
          baseListCopy.Add("Test2");
          baseListCopy.Add("Test3");
          baseListCopy.Add("Test4");
          baseListCopy.Add("Test5");
          baseListCopy.Add("Test6");
          baseListCopy.Add("Test7");
          baseListCopy.Add("Test8");
          baseListCopy.Add("Test9");
  
          List&lt;String&gt; resultListCopy = new List&lt;String&gt;();
          resultListCopy.Add("Test1");
          resultListCopy.Add("Test2");
          resultListCopy.Add("Test3");
          resultListCopy.Add("Test40");
          resultListCopy.Add("Test90");
  
          //returns only items that are present on both lists
          resultListCopy = baseListCopy.Intersect(resultListCopy, StringComparer.InvariantCultureIgnoreCase).ToList();
  
          //How do I return only items that are unique to that list?
  </code></pre>