`sig
val is_valid : year:int -> month:int -> day:int -> bool
val of_cjd :
?wday:int Pervasives.ref ->
?yday:int Pervasives.ref -> int -> int * int * int
val to_cjd : year:int -> month:int -> day:int -> int
val to_cjd_unsafe : year:int -> month:int -> day:int -> int
val of_mjd :
?wday:int Pervasives.ref ->
?yday:int Pervasives.ref -> int -> int * int * int
val to_mjd : year:int -> month:int -> day:int -> int
end`