Tolong jelaskan mengenai </div> dari Kidung Gregorian

H. Bewerung: "Kidung Geregorian", Catholic Encyclopedia William P. Mahrt: "Kidung Gregorian sebagai sebuah paradigma Musik Suci," Sacred Music, 133.3, halaman 5-14

Canticum Novum, Lessons on Gregorian Chant - Notation, characteristics, rhythm, modes, the psalmody and scores

Justine Ward, "The Reform of Church Music," Atlantic Monthly'', April 1906