r over a sequence being represented by <a href="http://msdn.microsoft.com/en-us/library/78dfe2yb.aspx">IEnumerator&lt;T&gt;</a>. </li> </ul>  <p>I fully expect that most readers will be comfortable with all of these concepts, so I won&#39;t go into them in more detail. If any of the above makes you nervous, please familiarise yourself with them before continuing, otherwise you&#39;re likely to have a hard time.</p>  <p>The purpose of &quot;Where&quot; is to filter a sequence. It takes an input sequence and 