title: Most efficient way to concatenate list within list without a loop
body: <pre><code>public class Unicorn
  {
      public List&lt;int&gt; Numbers { get; set; }
  }
  
  unicorns.Add(new Unicorn() { Numbers = {1, 2, 3} } );
  unicorns.Add(new Unicorn() { Numbers = {4, 5, 6} } );
  unicorns.Add(new Unicorn() { Numbers = {7, 8, 9} } );
  </code></pre>
  
  <p>What's the most efficient way in c# 4 to concatenate all the lists into one list of {1, 2, 3, 4, 5, 6, 7, 8, 9 } ?</p>
  
  <p>Preferably (ideally; by preference; if one had a choice) no loops and Linq-less. I tinkered around with .FindAll, but it's not digging it.</p>