1 (define (non-num-members as)
2   (filter (lambda (x) (not (number? x))) as))
3 (define (num-members as)
4   (filter number? as))
5 (define (more-than-one-number? as)
6   (let ((nums (num-members as)))
7     (if (or (null? nums) (null? (cdr nums)))
8 	#f
9 	#t)))
10 (define (zero-is-the-only-number? as)
11   (let ((nums (num-members as)))
12     (if (null? nums)
13 	#f
14 	(and (= (car nums) 0) (null? (cdr nums))))))
15 (define (one-is-the-only-number? as)
16   (let ((nums (num-members as)))
17     (if (null? nums)
18 	#f
19 	(and (= (car nums) 1) (null? (cdr nums))))))
20 (define (insert-signs result items sign)
21   (cond ((null? items) result)
22 	((null? result)
23 	 (insert-signs (list (car items)) (cdr items) sign))
24 	(else (insert-signs (append result (list sign (car items))) 
25 			    (cdr items) sign))))
26 
27