(let ((a 5)
      (b 2)
      )
  (display "a=") (displayln a)
  (display "b=") (displayln b)
  (define sum (+ a b))
  sum
  )

;(define (f a) (+ a b))

(letrec ((f (λ (x) (+ x y)))
         (y 5))
  ;(f 1)
  (define (x) (+ y 1))
  (define y 2)
  (x)
  )