+;;;###autoload
+(defun gnus-sorted-difference (list1 list2)
+ "Return a list of elements of LIST1 that do not appear in LIST2.
+Both lists have to be sorted over <.
+The tail of LIST1 is not copied."
+ (let (out)
+ (while (and list1 list2)
+ (cond ((= (car list1) (car list2))
+ (setq list1 (cdr list1)
+ list2 (cdr list2)))
+ ((< (car list1) (car list2))
+ (setq out (cons (car list1) out))
+ (setq list1 (cdr list1)))
+ (t
+ (setq list2 (cdr list2)))))
+ (nconc (nreverse out) list1)))
+
+;;;###autoload
+(defun gnus-sorted-ndifference (list1 list2)
+ "Return a list of elements of LIST1 that do not appear in LIST2.
+Both lists have to be sorted over <.
+LIST1 is modified."
+ (let* ((top (cons nil list1))
+ (prev top))
+ (while (and list1 list2)
+ (cond ((= (car list1) (car list2))
+ (setcdr prev (cdr list1))
+ (setq list1 (cdr list1)
+ list2 (cdr list2)))
+ ((< (car list1) (car list2))
+ (setq prev list1
+ list1 (cdr list1)))
+ (t
+ (setq list2 (cdr list2)))))
+ (cdr top)))
+
+;;;###autoload