(define append
  (lambda (l1 l2)
    (cond [(null? l1) l2]
	  [else (cons (car l1) (append (cdr l1) l2))])))

(define append2
  (lambda (l1 l2 r)
    (cond [(null? l1) r]
	  [else (append2 (cdr l1) l2 (cons (car l1) r))])))