Columbia subject headings:
Canon law--History.
Popes--Deposition.
Popes--Primacy.
Harvard subject headings:
Canon law--History.
Church history--Middle Ages, 600-1500
Church history--Primitive and early church, ca. 30-600
Popes--Deposition
Popes--Primacy
Princeton subject headings:
Canonists--10th century.
Canonists--11th century.
Papacy--History.
Popes--Primacy.