Albrecht Classen. 2019. “The Crisis of Spirituality in the Late Middle Ages: From the Twelfth Century to the Protestant Reformation; With an Emphasis on the Reformatio Sigismundi (1439)”. Global Journal of Human-Social Science 19 (D2):7-16. https://socialscienceresearch.org/index.php/GJHSS/article/view/2980.