1 (define (non-num-members as)
2   (filter (lambda (x) (not (number? x)))
3 	  as))
4 (define (num-members as)
5   (filter number? as))
6 (define (more-than-one-number? as)
7   (let ((nums (num-members as)))
8     (if (or (null? nums) (null? (cdr nums)))
9 	false
10 	true)))
11 (define (zero-is-the-only-number? as)
12   (let ((nums (num-members as)))
13     (if (null? nums)
14 	false
15 	(and (= (car nums) 0) (null? (cdr nums))))))
16 
17 (define (make-sum . as)
18   (cond ((null? as) 0)
19 	((null? (cdr as)) (car as))
20 	((null? (non-num-members as)) (apply + as))
21 	((more-than-one-number? as)
22 	 (apply make-sum
23 		(append (non-num-members as)
24 			(list (apply + (num-members as))))))
25 	((zero-is-the-only-number? as)
26 	 (apply make-sum (non-num-members as)))
27 	(else (append '(+) as))))
28 (define (make-product . ms)
29   (cond ((null? ms) 1)
30 	((null? (cdr ms)) (car ms))
31 	((null? (non-num-members ms)) (apply * ms))
32 	((more-than-one-number? ms)
33 	 (apply make-product
34 		(append (non-num-members ms)
35 			(list (apply * (num-members ms))))))
36 	((zero-is-the-only-number? ms) 0)
37 	((one-is-the-only-number? ms)
38 	 (apply make-product (non-num-members ms)))
39 	(else (append '(*) ms))))
40 
41 
42 (define (augend s)
43   (apply make-sum (cddr s)))
44 (define (multiplicand p)
45   (apply make-product (cddr p)))