(setq A '(1 2 3 4 5))

(setq newlist '())

(defun caesar (X newlist d)
 (if (cdr X)
      (progn
       (push (+ (car X) d) newlist)
       (caesar (cdr X) newlist d)
      )
     (push (+ (car X) d) newlist)
     (reverse newlist)
 )
)

(message "%S wird zu %S" A (caesar A newlist 3))