title: Group by multiple keys and ignore case
body: <p>When I try to do the following,</p>
  
  <pre><code>collection.GroupBy(item =&gt; new
                          {
                              item.Item1,
                              item.Item2,
                              item.Item3,
                              item.Item4
                          }, StringComparer.CurrentCultureIgnoreCase)
  </code></pre>
  
  <p>I get an error that the argument types cannot be inferred from the usage, and to try to specify the type arguments explicitly.</p>
  
  <p>What is the right syntax for this?</p>