4Peter Wagner, Einfhrung in die gregorianischen Melodien, vol. I (Fribourg, 1895 ) ; vol. 2 (Fribourg, 1905, 2/1912/ R1962).
5vol. 3 (Leipzig, 1921/R 1962), see Ruth Steiner, "Gregerian Chant", Bibliography, in Stanley Sadie ed. , The New Grove Dietionnary of Music and Musicians, London: Macmillan Publishers Ltd. , 1980, vol. 7, p. 698.
6Kay K. Shelemay, Peter Jeffery , Ingrid Monson, "Oral and Written Transmission in Ethiopian Christian Chant", Early Mu- sicHistory (12), 1993, pp. 55-117.
7Peter Jef- fery, Re-Envisioning Past Musical Cultures-Ethnomusicology in the Study of Gregorian Chant, Chicago : the University of Chi- cago Press, 1992.
8Anna Maria Busse Berger, Medieval Music and the Art of Memory, Berkeley and Los Angeles: University of California Press, 2005.
