title: Check if two list have the same items
body: <p>I have two lists as below, how can I say that they have the same elements. The order is not important.</p>
  
  <pre><code>var list1 = new List&lt;int&gt; {1,2,3};
  var list2 = new List&lt;int&gt; {2,1,3};
  </code></pre>
  
  <p>How can I say that these are equal? Should I write my own method or is there a built-in method for it?</p>