Hiley, David. 1981. The Liturgical Music of Norman Sicily: A Study centered on Manuscripts 288, 289, 19421 and Vitrina 20-4 of the Biblioteca Nacional, Madrid. PhD thesis, King's College, University of London, May 1981.
The liturgy of Ravenna Chant (usually discussed as "rîte d'Aquilea" in French, and as "rito patriarchino" in Italian studies) has only survived in small parts by the written transmission of notated manuscripts.
Bibiana Gattozzi has written a very interesting master thesis about the origin and the destination(s) of the 12th-century gradual-proser 35 (please have a look at the announcement with the official link).
