title: filter a list of lists : basic thing
body: <p>Do you know why this program does not give expected answer <code>(List(3,3))</code> ?</p>
  
  <pre><code>val l=List(List(1,2),List(3,3))
  println(l.filter(_ match{
      case u::v =&gt; u==v
      case _ =&gt; false
  }))
  </code></pre>
  
  <p>thanks!</p>