APA (7th ed.) Citation

Spence, R. T. (1981). Pope Gregory the ninth and the crusade. Univ. Microfilms Internat.

Chicago Style (17th ed.) Citation

Spence, Richard T. Pope Gregory the Ninth and the Crusade. Ann Arbor, MI: Univ. Microfilms Internat, 1981.

MLA (9th ed.) Citation

Spence, Richard T. Pope Gregory the Ninth and the Crusade. Univ. Microfilms Internat, 1981.