title: How to yield a nested IENumerable?
body: <p>I know how to yield values in a method with return value <code>IENumerable</code></p>
  
  <pre><code>public IEnumerable&lt;int&gt; GetDigits()
  {
      yield return 1;
      yield return 1;
      yield return 1;
  }
  </code></pre>
  
  <p>but how is the correct Syntax for a nested <code>IEnumerable&lt;IEnumerable&lt;int&gt;&gt;</code>?</p>
  
  <pre><code>public IEnumerable&lt;IEnumerable&lt;int&gt;&gt; GetNestedDigits()
  {
      yield return yield return 1; //??
  }
  </code></pre>