title: enum casting (compile and does not compile)
body: <p>Why does addition require a cast?<br>
  <strong>Any help?</strong> </p>
  
  <pre><code>public enum _enum
  {
      A = 12,
      B = 20,
      C = 30
  }
  
  var Sub = _enum.A - _enum.B; // Compiles
  var Add = _enum.A + _enum.B; // Does not compile
  var Add2 = (int)_enum.A + _enum.B; // Compiles  
  </code></pre>