(defun compress ( l )

  (cond

   ((null l) l)
   
   (t (compress1 (car l) 1 (cdr l)))))



(defun compress1 (a n l)

  (cond

   ((null l) (if (> n 1)
                 
                 (list a n)

               (list a)))

   ((eql (car l) a) (compress1 a (+ n 1) (cdr l)))

   (t (cons 

       (if (> n 1)

           (list a n)

         a)

       (compress1 (car l) 1 (cdr l))))))