La Trobe University - Library: Medieval Music Database - Annual cycle of feasts of liturgical chant, liturgical polyphony and secular music of the late middle ages.

Kyrie, Orbis factor?

anonymous

Stratford: Shakespeare Birthplace Library, Archer 41 (olim Archer 2), fol. 2v.

XIvth and Early XVth Century English Polyphony, Russell Oberlin (C-T), Charles Bressler (T), Gordon Myers (B: Expèriences Anonymes EA 31.