title: How come I don't need to reference "System.dll" to use the "System" namespace?
body: <p>I am working on an assignment that specified "Do not use any external libraries". So I created a c# application, and the first thing I did was remove all the dll's references by default... including "System.dll".</p>
  
  <p>However, I can still add this to my code:</p>
  
  <pre><code>using System;
  using System.IO;
  </code></pre>
  
  <p>I was just curious as to how come I do not need to have System.dll as a reference in my project to do this. Thanks!</p>