title: The type or namespace name 'Stack' could not be found (only with .NET 4.0)
body: <p>I get an error when i compile this program:</p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  
  static class main {
      public static void Main() {
          Stack&lt;int&gt; a;
      }
  };
  </code></pre>
  
  <p>with this cmd:</p>
  
  <p><code>C:\Users\tomc\Desktop\l&gt;C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc test.cs</code></p>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>test.cs(12,3): error CS0246: The type or namespace name 'Stack' could not be
            found (are you missing a using directive or an assembly reference?)</p>
  </blockquote>
  
  <p>However when using this command it builds fine:
  <code>C:\Users\tomc\Desktop\l&gt;C:\Windows\Microsoft.NET\Framework64\v3.5\csc test.cs</code></p>
  
  <p><strong>Was Stack removed from .NET 4 ? I can't find any indication that it was on MSDN.</strong></p>