(define (map fun list)
  (if (null? list) '()
      (cons (fun (car list)) (map fun (cdr list)))))

(define (filter p? list)
  (if (null? list) '()
      (if (p? (car list)) (cons (car list) (filter p? (cdr list))) (filter p? (cdr list)))))

(define (accumulate op nv a b term next)
  (if (> a b)
      nv
      (op (term a)
          (accumulate op nv (next a) b term next))))