n that iterator, we <em>should</em> start iterating, causing an exception to be thrown. </li> </ul>  <p>We&#39;ll need to do something similar for other operators, so I&#39;ve written a small helper method in ThrowingEnumerable:</p>  <div class="code"><span class="Modifier">internal</span>&#160;<span class="Modifier">static</span>&#160;<span class="ValueType">void</span> AssertDeferred&lt;T&gt;(     <br />&#160;&#160;&#160; Func&lt;IEnumerable&lt;<span class="ValueType">int</span>&gt;, IEnumerable&lt;T&gt;&