3IF. Alberto Gallo, Musicofthe Middle Ages, Volume Ⅱ, Cambridge: Cambridge University Press, 1977,p163.
4Cattin, Giulio, Music of the Middle Ages, Volume Ⅰ, Cambridge University of Press, 1984, p8.
5Seay, Albert. Music in the Medieval World, Second Edition, Prentice Hall History of Music Series, Englewood Cliffs, New Jersey:prentice-hall, inc., 1975, p93.
