Atkinson, Charles Monte. 2001. The Other Modus: On the Theory and Practice of Intervals in the Eleventh and Twelfth Centuries. The Study of Medieval Chant: Paths and Bridges, East and West: In Honour of Kenneth Levy, edited by Charles Monte Atkinson, 233-56. Woodbridge: Boydell Press.

Jeffery, Peter. 1984. A Four-Part 'In seculum' Hocket and a Mensural Sequence in an Unknown Fragment. JAMS, 1-48.