*Rosenthal, H. and Warrack, J., "Betz, Franz", "The Concise Oxford Dictionary of Opera", 2nd Edition, Oxford University Press, 1979, p. 49.
* Rosenthal, H. and Warrack, J., «Betz, Franz», "The Concise Oxford Dictionary of Opera", 2nd Edition, Oxford University Press, 1979, p. 49.