title: yield return multiple IEnumerables
body: <p>I have a test function that returns an <code>IEnumerable</code>, which inside, I want to <code>yield return</code> other functions that return <code>IEnumerable</code>.</p>
  
  <pre><code>public IEnumerable Foo()
  {
      Console.WriteLine("Foo!");
      yield break;
  }
  
  public IEnumerable Bar()
  {
      Console.WriteLine("Bar!");
      yield break;
  }
  
  public IEnumerable Foobar()
  {
      foreach (var o in Foo())
      {
          yield return o;
      }
  
      foreach (var o in Bar())
      {
          yield return o;
      }
  }
  </code></pre>
  
  <p>However, this "Foobar" function will have many more inner functions that return IEnumerable.</p>
  
  <p>Is there any shorter way to do this instead of having to <code>foreach</code> and iterate over very function?</p>