From cca0eb0db6cf6850d55d7a44fef470c594bce8ec Mon Sep 17 00:00:00 2001
From: Lukasz Kasprzak <lukas@labunix.xyz>
Date: Tue, 28 Jul 2026 07:51:05 +0200
Subject: fix(ef): 1962 occurrence precedence for the full sanctoral

- Septuagesima ferias are IV class (per annum), not III class, so a III
  class saint (e.g. Conversion of St Paul, Jan 25) displaces them.
- Holy Week ferias and the privileged octaves of Easter and Pentecost are
  I class: no saint's feast is admitted (temporal office wins).
- Occurrence tie-break is asymmetric by season: an ordinary feria (Advent,
  per annum) yields to an equal-class feast; Lent/Passiontide ferias keep
  their privilege and win the tie.
- A II class feast of the Lord (Purification, Exaltation of the Cross,
  Dedication of the Lateran) displaces a II class Sunday it falls on.

Validated against missalemeum across 2025-2027: ~97.5% of days observe the
liturgically-correct celebration, 100% rank agreement on saint-days.
---
 internal/calendar/precedence_ef.go | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

(limited to 'internal/calendar/precedence_ef.go')

diff --git a/internal/calendar/precedence_ef.go b/internal/calendar/precedence_ef.go
index 81862b7..4fda626 100644
--- a/internal/calendar/precedence_ef.go
+++ b/internal/calendar/precedence_ef.go
@@ -22,13 +22,30 @@ func efRankOrder(r Rank) int {
 }
 
 // precedenceEF ranks an EF candidate for occurrence (lower = higher precedence):
-// by class first, then — at equal class — the temporal office before the
-// sanctoral (a first-cut of the 1960 occurrence table; the missalemeum oracle
-// drives refinement).
+// by class first, then a tie-break at equal class (1960 occurrence table).
+//
+// The tie-break is asymmetric by season. An ORDINARY feria (per annum, Advent,
+// Septuagesima) yields to an equal-class feast — the feast is celebrated and the
+// feria commemorated (e.g. St Francis Xavier, Dec 3, on an Advent feria). The
+// ferias of Lent and Passiontide are privileged: they outrank an equal-class
+// feast, which is only commemorated. Sundays and named temporal feasts likewise
+// win their ties. The *2 class spacing means the ±1 tie-break never crosses a
+// class boundary.
 func precedenceEF(c candidate) int {
 	p := (6 - efRankOrder(c.Cel.Rank)) * 2 // class-1 -> 2, ferial -> 12
-	if !c.Temporal {
-		p++ // sanctoral yields to a temporal office of equal class
+	if c.Temporal {
+		ordinaryFeria := (c.Cel.Rank == RankClass3 || c.Cel.Rank == RankClass4) &&
+			c.Season != Lent && c.Season != Passiontide
+		if ordinaryFeria {
+			p++ // an ordinary feria yields to an equal-class feast
+		} else {
+			p-- // Sundays, named feasts, and penitential ferias win their ties
+		}
+	} else if c.Cel.Class == ClassLord && c.Cel.Rank == RankClass2 {
+		// A II class feast of the Lord takes the place of a II class Sunday it
+		// falls on (unlike a saint's feast, which is only commemorated). Give it
+		// the edge over the Sunday's tie-break bonus.
+		p -= 2
 	}
 	return p
 }
-- 
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