title: List of lists in racket
body: <p>I need to create this:</p>
  
  <p>Define a min&amp;max-lists function that consumes a list of lists
  (where the type of the elements in the inner list may be any type).</p>
  
  <p>The function returns a list of lists – such that for each inner list (in the
  original list) the following is done – </p>
  
  <ol>
  <li>If the list contains at least one number, then the list is replaced with a list of size two, containing the minimum and maximum in the list.</li>
  <li>Otherwise, the list is replaced with a null.</li>
  </ol>
  
  <p><strong>For example</strong></p>
  
  <p>written in a form of a test that you can use:</p>
  
  <pre><code>(test (min&amp;max-lists '((any "Benny" 10 OP 8) (any "Benny" OP (2 3)))) 
  </code></pre>
  
  <p>=> '((8 10) ()))
      (test (min&amp;max-lists '((2 5 1 5 L) (4 5 6 7 3 2 1) ())) >> '((1 5) (1 7) ()))</p>
  
  <p>For now, I have created a function that do it for one list.</p>
  
  <p>How I do it for the list of lists??</p>
  
  <p><strong>for example:</strong></p>
  
  <pre><code>(listhelp '(2 5 1 5 L)) 
  -&gt; : (Listof Number)&gt;&gt;'(1 5)
  </code></pre>