title: The type or namespace name 'SortedSet' could not be found
body: <p>I'm trying to use SortedSet in a simple console application (using .NET 4.7.2) but for some reason it is not contained in <code>System.Collections.Generic</code> namespace. </p>
  
  <p>That being said HashSet is there and works perfectly fine.
  According to documentation <a href="https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic?view=netframework-4.7.2" rel="nofollow noreferrer">here</a> they're both in the same namespace, so I'm completely lost why one is there and the other isn't. If anyone has any suggestions I'd be glad to try them.</p>
  
  <p>Here's my code:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  
  namespace TextProcessor
  {
      class App
      {
          static void Main(string[] args)
          {
              HashSet&lt;string&gt; set = new HashSet&lt;string&gt;();
              SortedSet&lt;string&gt; sortedset = new SortedSet&lt;string&gt;();
              Console.ReadKey();
          }
      }
  }
  </code></pre>