+ ; (aver (equal (mapcar #'car pairs)
+ ; (sort (mapcar #'car pairs) #'<)))
+ ;; aver that the cars of the list elements are sorted into increasing order
+ (aver (or (null pairs)
+ (do ((p pairs (cdr p)))
+ ((null (cdr p)) t)
+ (when (> (caar p) (caadr p)) (return nil)))))