Columbia subject headings:
Catholic Church--History--Sources.
Holy Roman Empire--History--Otto IV, 1198-1215--Sources.
Harvard subject headings:
Canon law.
Catholic Church--History--Sources.
Holy Roman Empire--History--Otto IV, 1198-1215--Sources.
Princeton subject headings:
Catholic Church--History--Sources.
Holy Roman Empire--History--Otto IV, 1198-1215--Sources.