#| BEGIN (Write your solution here) |#
(define (count-leaves t)
  (accumulate + 0 (map (lambda (n) (if (pair? n)
                                       (count-leaves n)
                                       1))
                       t)))

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