om here, it&#39;s a short step to implement the version using an index as well:</p>  <div class="code"><span class="Modifier">public</span>&#160;<span class="Modifier">static</span> IEnumerable&lt;TSource&gt; Where&lt;TSource&gt;(     <br />&#160;&#160;&#160; <span class="Keyword">this</span> IEnumerable&lt;TSource&gt; source,     <br />&#160;&#160;&#160; Func&lt;T, <span class="ValueType">int</span>, <span class="ValueType">bool</span>&gt; predicate)     <br />{     <br />&#160;&#160;&#160; <span class="St