APA

Ullmann W., . (1966). Principles of government and politics in the Middle Ages. New York: Barnes & Noble.

Chicago

Ullmann Walter, . 1966. Principles of government and politics in the Middle Ages. New York: Barnes & Noble.

Harvard

Ullmann W., . (1966). Principles of government and politics in the Middle Ages. New York: Barnes & Noble.

MLA

Ullmann Walter, . Principles of government and politics in the Middle Ages. New York: Barnes & Noble. 1966.