(** RG 475-476 (docs/research/LT.txt, grep "dicitur symbolum") -- whether the
    Creed is said at Mass. The first rubric in this phase governing a PART OF
    MASS rather than occurrence/precedence, hence its own module: see the
    .ml's own header for the rubric quoted in full and every branch's
    citation. *)

open Colitur_kernel

(** RG 475(e)'s "festis nataliciis Apostolorum et Evangelistarum, necnon in
    festis Cathedrae S. Petri et S. Barnabae Ap." -- see the .ml's own
    citation for how each entry was derived from and verified against
    data/ef/sanctoral.sexp, and for what was deliberately excluded. Exposed
    so the test suite can assert completeness against the shipped data the
    same way {!Precedence_ef.vigil_feast_table} already lets it. *)
val creed_apostle_slugs : string list

(** Whether the Creed is said, post-Gospel/homily, at the Mass this day
    resolves to.

    [temporal] is read for exactly one fact -- RG 475(a)'s own "in qualibet
    dominica, ETSI EIUS OFFICIUM ALICUI FESTO LOCUM CEDAT" ("on any Sunday,
    EVEN WHEN a feast displaces its own Office"): a Sunday impeded by a
    Feast of the Lord (RG 16(a)) still says the Creed, so this reads the
    TEMPORAL cycle's own weekday, never [observed]'s. Every other clause
    reads [observed] -- the celebration whose Mass is actually said -- and
    [date], read once against the rite's own (Gregorian) Easter for the two
    Easter-relative window questions (RG 475(d)'s three octaves, RG 23's
    Ash-Wednesday-and-Holy-Week feriae). [creed] never reads
    {!Liturgical_day.t.commemorations}: RG 476(e), "ratione alicuius
    commemorationis in Missa occurrentis" [never say the Creed merely
    because of a commemoration], holds by construction rather than by a
    checked branch. RG 476(f) ("in Missis defunctorum") reads
    [observed]'s [colour]: see the .ml's own header for why [Colour.Black]
    is a sound proxy for "this Mass is a Requiem" on the shipped data, and
    what would have to be re-checked if that ever stops being true. *)
val creed :
  temporal:(Vocab_ef.season, Vocab_ef.rank) Temporal.t ->
  observed:Vocab_ef.rank Celebration.t ->
  date:Date.t ->
  bool