Tolong jelaskan mengenai Catatan dari Wala dari Corbie

Mayr-Harting, Henry (1990). “Two Abbots in Politics: Wala of Corbie and Bernard of Clairvaux.” Transactions of the Royal Historical Society, Fifth Series, vol. 40.

Riché, Pierre (1993). The Carolingians: A Family who Forged Europe. Philadelphia: University of Pennsylvania Press. .

McKitterick, Rosamond (2008). Charlemagne: The Formation of a European Identity. Cambridge University Press.

Nelson, Janet. (2010). The Frankish World, 750–900. Continuum International Publishing.