1. Aziz, A. K., Gilbert, R. P., Howard, H. C. : On a Non-linear Elliptic Boundary Value Problem with Generalized Goursat Data. Tech. Note BN-377, Univ. of Maryland, Sept. 1964.
2. Bergman, S. : Two-Dimensional Transonic Flow Patterns. Amer.J.Math.70, 1948, pp. 856–891.
3. Bergman, S. : On Solutions of Linear Partial Differential Equations of Mixed Type. Amer. J. Math. 74, 1952, pp.444–474.
4. Bergman, S. : Integral Operators in the Theory of Linear Partial Differential Equations. Springer-Verlag, Berlin-Goettingen-Heidelberg, 1961.
5. Bergman, S. : On Value Distribution of Meromorphic Functions of Two Complex Variables. Studies in Mathematical Analysis and Related Topics. (Ed. by Gilbarg, D., Solomon, H, et al.), Stanford Univ. Press, 1962.