S-99-61

(define (count-leaves T)

  (define (tree-left T) (cadr T))
  (define (tree-right T) (caddr T))

  (cond ((null? T) 0)
        ((and (null? (tree-left T)) (null? (tree-right T))) 1)
        ((else (+ (count-leaves (tree-left T)) (count-leaves (tree-right T))))
  )

)