Exercise 1.33. You can obtain an even more general version of accumulate (exercise 1.32) by introducing the notion of a filter on the terms to be combined. That is, combine only those terms derived from values in the range that satisfy a specified condition. The resulting filtered-accumulate abstraction takes the same arguments as accumulate, together with an additional predicate of one argument that specifies the filter. Write filtered-accumulate as a procedure. Show how to express the following using filtered-accumulate:

a. the sum of the squares of the prime numbers in the interval a to b (assuming that you have a prime? predicate already written)

b. the product of all the positive integers less than n that are relatively prime to n (i.e., all positive integers i < n such that GCD(i,n) = 1).

(define (filtered-accumulate combiner null-value term a next b filter)
  (define (iter a result)
    (if (> a b)
	result
	(iter (next a) (combiner 
			(if (filter a) 
			    (term a)
			    null-value)
			    result))))
  (iter a null-value))
 
 
 
 
(define (prime-squared-sum a b)
  (filtered-accumulate + 0 square a inc b prime?))