title: Combine lists that have at least a number in common in a list of lists, Python
body: <p>Consider this list of lists:</p>
  
  <pre><code>l = [ [1], [1], [1,2,3], [4,1], [5], [5], [6], [7,8,9], [7,6], [8,5] ]
  </code></pre>
  
  <p>I want to combine all the lists that have at least one number in common, that will be done iteratively until it finished and no dubletters will go with. The result will be:</p>
  
  <pre><code>combine(l) = [ [1,2,3,4], [5,6,7,8,9] ]
  </code></pre>
  
  <p>is there any neat way to do this, perhaps with itertools?</p>