title: RoutedEventArgs cannot be founded in the System.Windows
body: <p>I have a program on the Windows Forms (VS13). In the code:</p>
  
  <pre><code>using System.Windows;
  
  namespace WF
  {
      public partial class Form1 : Form
      {
          private void Window_Loaded(object sender, RoutedEventArgs e)
          {
              //...
          }
      }
  }
  </code></pre>
  
  <p><code>RoutedEventArgs</code> cannot be found, but it exists in the namespace <code>System.Windows</code>. What can be reason? I have a reference to the <code>WindowsBase</code>.</p>