Catherine. Chant: The Origins, Form, Practice, and Healing Power of Gregorian Chant. Harmony. 1994. ISBN 0-517-70037-9. Mahrt, William P. (2000). Chant. In
ISBN 2-85274-219-5, facsimiles of early adiastamatic chant manuscripts Apel, Willi. Gregorian Chant. Bloomington, IN: Indiana University Press. 1990. ISBN