Weeks, Gregory (1999). "Ritter, Gerhard A." In Kelly Boyd, ed., The Encyclopedia of Historians and Historical Writing. Chicago: Fitzroy Dearborn Publishers, p. 996.
Weeks, Gregory (1999). "Ritter, Gerhard A." In Kelly Boyd, ed., The Encyclopedia of Historians and Historical Writing, Chicago: Fitzroy Dearborn Publishers, p. 997.