Ullmann, W. (1978). Principles of government and politics in the Middle Ages. Methuen.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रUllmann, Walter. Principles of Government and Politics in the Middle Ages. Methuen, 1978.
एमएलए (9वां संस्करण) प्रशस्ति पत्रUllmann, Walter. Principles of Government and Politics in the Middle Ages. Methuen, 1978.
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