(define my-append
  '(lambda-rec (append xs ys)
               (if (null? xs)
                   ys
                   (cons (car xs) (append (cdr xs) ys)))))

(define my-map
  '(lambda-rec (map f xs)
               (if (null? xs)
                   null
                   (cons (f (car xs))
                         (map f (cdr xs))))))

(define my-reverse
  '(lambda (xs)
     ((lambda-rec (iter xs ys)
                  (if (null? xs)
                      ys
                      (iter (cdr xs) (cons (car xs) ys))))
      xs null)))