title: how to test if an integer is in a sub-list in a list
body: <p>I'd like to test if 3 is the first number of the element (an integer or the first of a sub-list) like this :</p>
  
  <pre><code>lst=[2, [3,6], [4,1,7]]
  3 in lst
  </code></pre>
  
  <p>The result should be True because 3 is the first element of [3,6].</p>
  
  <p>Btw: my dataset won't make my list like [3, [3,7]] (alone and in a sublist)</p>