1 (define (search f neg-point pos-point)
2   (let ((midpoint (average neg-point pos-point)))
3     (if (close-enough? neg-point pos-point)
4 	midpoint
5 	(let ((test-value (f midpoint)))
6 	  (cond ((positive? test-value)
7 		 (search f neg-point midpoint))
8 		((negative? test-value)
9 		 (search f midpoint pos-point))
10 		(else midpoint))))))