diff -r6.12 gnus-range.el
63a64,104
> (defun gnus-range-difference (range1 range2)
>   "Return the range of elements in RANGE1 that do not appear in RANGE2.
> Both ranges must be in ascending order."
>   (setq range1 (gnus-range-normalize range1))
>   (setq range2 (gnus-range-normalize range2))
>   (let* ((new-range (cons nil (copy-sequence range1)))
>          (r new-range)
>          (safe t))
>     (while (cdr r)
>       (let* ((r1 (cadr r))
>              (r2 (car range2))
>              (min1 (if (numberp r1) r1 (car r1)))
>              (max1 (if (numberp r1) r1 (cdr r1)))
>              (min2 (if (numberp r2) r2 (car r2)))
>              (max2 (if (numberp r2) r2 (cdr r2))))
> 
>         (cond ((> min1 max1)
>                ;; Invalid range: may result from overlap condition (below)
>                ;; remove Invalid range
>                (setcdr r (cddr r)))
>               ((and (= min1 max1)
>                     (listp r1))
>                ;; Inefficient representation: may result from overlap condition (below)
>                (setcar (cdr r) min1))
>               ((not min2)
>                ;; All done with range2
>                (setq r nil))
>               ((< max1 min2)
>                ;; No overlap: range1 preceeds range2
>                (pop r))
>               ((< max2 min1)
>                ;; No overlap: range2 preceeds range1
>                (pop range2))
>               ((and (<= min2 min1) (<= max1 max2))
>                ;; Complete overlap: range1 removed
>                (setcdr r (cddr r)))
>               (t
>                (setcdr r (nconc (list (cons min1 (1- min2)) (cons (1+ max2) max1)) (cddr r)))))))
>     (cdr new-range))
>   )
>