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; see: https://mitpress.mit.edu/sicp/chapter1/node9.html
(define square
(lambda (x)
(* x x)))
(define average
(lambda (x y)
(/ (+ x y) 2)))
(define improve
(lambda (guess x)
(average guess (/ x guess))))
(define good-enough?
(lambda (guess x)
(< (abs (- x (square guess)))
0.001)))
(define sqrt-iter
(lambda (guess x)
(if (good-enough? guess x)
guess
(sqrt-iter (improve guess x) x))))
(define test-sqrt
(lambda (x)
(sqrt-iter 1.0 x)))
(test-sqrt 9)
; => 3.00009155413138
(test-sqrt (+ 100 37))
; => 11.704699917758145
(test-sqrt (+ (test-sqrt 2) (test-sqrt 3)))
; => 1.7739279023207892
(square (test-sqrt 1000))
; => 1000.000369924366
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