#| BEGIN (Write your solution here) |#
(define (map p sequence)
  (accumulate (lambda (x y) (cons (p x) y)) nil sequence))

(define (append seq1 seq2)
  (accumulate cons seq2 seq1))

(define (length sequence)
  (accumulate (lambda (_ s) (+ s 1)) 0 sequence))

(define (accumulate op initial sequence)
  (if (null? sequence)
      initial
      (op (car sequence)
          (accumulate op initial (cdr sequence)))))
#| END |#