title: List.Contains doesn't work properly
body: <p>I have a list which contains objects but these objests aren't unique in the list. I wrte this code to make unique them in another list:</p>
  
  <pre><code> foreach (CategoryProductsResult categoryProductsResult in categoryProductsResults.Where(categoryProductsResult =&gt; !resultSet.Contains(categoryProductsResult)))
   {
      resultSet.Add(categoryProductsResult);
   }
  </code></pre>
  
  <p>But at the end resultSet is the same with categoryProductsResults. </p>
  
  <p>categoryProductsResult's second row :</p>
  
  <p><img src="https://i.stack.imgur.com/lu8XY.png" alt="enter image description here"></p>
  
  <p>resultSet first row:</p>
  
  <p><img src="https://i.stack.imgur.com/dhFUk.png" alt="enter image description here"></p>
  
  <p>As you can see resultSet's first row and categoryProductsResult's second row is the same but it adds the second row to resultSet.</p>
  
  <p>Do you have any suggestion?</p>