minta zh 2. feladat

(defun swap (l p1 p2)
(let ( (s1 (nth (1- p1) l)) (s2 (nth (1- p2) l)))
(setf (nth (1- p1) l) s2) (setf (nth (1- p2) l) s1) l ; this l is the returned value
)
)