(define list-of-numbers?
    (lambda (lst)
      (if (null? lst)
	  #t
	  (if (pair? lst)
	      (if (number? (car lst))
		  (list-of-numbers? (cdr lst))
		  #f)
	      #f))))

    Source: geocities.com/siliconvalley/way/5970

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