Gaya APA
Ullmann, W. (1966).
Principles of government and politics in the Middle Ages, [2nd ed.]. Tjet.pertama 1961. .
London:
Methuen.
Gaya MLA
Ullmann, Walter..
"Principles of government and politics in the Middle Ages, [2nd ed.]. Tjet.pertama 1961. ".
London:
Methuen,
1966.
Buku.