I've been trying to do a function that returns the Cartesian Product of n sets,in Dr Scheme,the sets are given as a list of lists,I've been stuck at this all day,I would like a few guidelines as where to start,I've wrote a pice of code but it dosen't work.

(define cart-n(?(l)
          (if (null? l)  '(())
              (map
               (?(lst) (cons (car ( car(l))) lst))
               (cart-n (cdr l) )))))