;(define (count-leaves x)
;  (cond ((null? x) 0)
;        ((not (pair? x)) 1)
;        (else (+ (count-leaves (car x))
;                 (count-leaves (cdr x))))))

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


(define (count-leaves x)
  (accumulate + 0 (map (lambda (y) 
			 (if (not (pair? y)) 
			     1 
			     (+ (count-leaves (car y))
				(count-leaves (cdr y))))) x)))