Structure and interpretation of computer programs (SICP)

(
 define (good-enough? guess x)
 (< (abs (- (square guess) x)) 0.001))
(
 define (average x y)
 (/ (+ x y) 2))
(
 define (improve guess x)
 (average guess (/ x guess)))
(
 define (sqrt-iter guess x)
  (if (good-enough? guess x)
    guess
    (sqrt-iter (improve guess x)
               x)))

; Or we can use block structure...
(define (sqrt x)
  (define (returns-one x)
    1)
  (sqrt-iter (returns-one 500) x))






```scheme
(define (f x)
  (+ x (let ((a 3) (b 4)) (+ a b)))
  )

(define (add_one y)
  (
   (lambda (b) (+ b 1)) y
))

(define (sqr x) (
    (lambda (x) (* x x)) x
))