I-AO 6
Early thirteenth-century antiphoner said to be from the Collegiate church of Sant’Orso (St. Ours), Aosta. Square neumes on a four-line staff with F and/or C clefs; the F line is coloured. Cathedral cursus. 143 folios. One lacuna (after f. 89). Begins at Passion Sunday.
Liturgical occasions: 
Ff. 1-45: Summer Temporale. 1r, Passion Sunday; 13v, Easter; 23v, Ascension; 26v, Pentecost; 29r, Trinity; 31v, Histories; 41v, Sundays after Pentecost. Ff. 45-120: Sanctorale. 45v, Dedication of a Church; 48r, Conception of Mary; 51r, Agnes; 89r, Augustine; 98v, Michael; 102v, Gall; 105r, Simon & Jude; 106v, All Saints; 109v, Office for the Dead; 112r, Martin. Ff. 120-133: Common of Saints. 120v, Common of Apostles; 131v, Common of Virgins. Ff. 133-140: Invitatory Tones. Ff. 141-143: Additamenta. 141r, Fabian & Sebastian, 143r, Mass chants.

At one time, this manuscript was part of a larger book. (See the earlier layer of foliation on some folios: f. 31r which was at one time f. lxxxv, for example.) F. 12 is out of place; it belongs before the present f. 1.

Many of the differentiae in this manuscript have been redrawn or erased. The differentiae of each mode have been numbered with a two-digit system: an upper-case letter indicating the final pitch of the differentia and a sequentially ordered numeral.

Chants not found in CAO have been assigned arbitrary numbers beginning with “our.”

Indexing notes: 
The index for I-AO 6 was prepared by Andrew Mitchell and Debra Lacoste at the University of Western Ontario.