title: functions and lists in scheme/racket
body: <p>How would you define a function which takes one argument, which should be a list, and returns the elements in the
  list which are themselves lists?</p>
  
  <pre><code>(check-expect (find-sublists ’(1 2 () (3) (a b c) a b c)) 
                ’(() (3) (a b c)))
  </code></pre>