(o1 (nndiary-next-occurence s1 now))
(o2 (nndiary-next-occurence s2 now)))
(if (and (= (car o1) (car o2)) (= (cadr o1) (cadr o2)))
- (< (mail-header-number h1) (mail-header-number h2))
+ (< (mail-header-number h1) (mail-header-number h2))
(time-less-p o1 o2))))