First reference:
Book: Kreuser, Johann (1854). Das Heilige Messopfer: geschichtlich erklärt. Bayerische Staatsbibliothek, page 98
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Second reference:
Article in journal: Frothingham, Arthur Lincoln (1885). Arnolfo di Lapo († 1310) and Jacopo Torriti at Rome. The American Journal of Archaeology and of the History of the Fine Arts, Vol. 1, No. 1: pp. 54-56
Link: