#lang scheme

(define test-expr
  (lambda (make-lit make-sub)
    (make-sub (make-sub (make-lit 6) (make-lit 1))
              (make-sub (make-lit 3) (make-lit 2)))))

(define eval-big
  (lambda (e)
    (e (lambda (n) n)
       (lambda (e1 e2) (- e1 e2)))))