+class status :
+ object ('self)
+ method timestamp: timestamp
+ method set_timestamp: timestamp -> 'self
+ method set_library_status: <timestamp: timestamp; ..> -> 'self
+ end
+
+(* it also checks it and add it to the environment *)
+val add_obj: #status as 'status -> NCic.obj -> 'status
+val add_constraint:
+ #status as 'status -> bool -> NCic.universe -> NCic.universe -> 'status