+type time
+
+val start_time : unit -> time
+
+val stop_time : time -> string
+
+type 'a comparison = Lt
+ | Gt
+ | Eq of 'a
+
+val list_join : ('a -> 'a -> 'a comparison) -> 'a list -> 'a list -> 'a list
+
+val list_meet : ('a -> 'a -> 'a comparison) -> 'a list -> 'a list -> 'a list
+