Why do types referenced outside of a namespace need to be fully qualified?
<p>Given the following code snippet:</p>

<pre><code>using System;

using Foo = System.Int32;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
        }
    }
}
</code></pre>

<p>If I remove the "System." from in front of Int32 in my declaration for the "Foo" type alias, I get a compiler error. Despite the fact that I'm using the System namespace at the top of the file, the compiler can't find an unqualified "Int32" type.</p>

<p>Why is that?</p>
