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+open Sexplib0.Sexp_conv
+
+(* The temporal identity of a date: where in the liturgical year it sits, and
+   the temporal cycle's own office for it. *)
+type ('s, 'r) t = {
+  season : 's;
+  week : int option;  (** [None] for named days outside a numbered week *)
+  weekday : Date.weekday;
+  office : 'r Celebration.t;
+}
+[@@deriving sexp]
+
+module type RITE = sig
+  val id : string
+
+  type season
+  type rank
+
+  val vocab : (season, rank) Vocab.t
+
+  (** First day of the liturgical year opening in civil year [y]. *)
+  val year_start : int -> Date.t
+
+  (** Total over 1583..9999: every date yields exactly one temporal identity. *)
+  val temporal : Date.t -> (season, rank) t
+end