1. H. Begehr, Complex Analytic Methods for Partial Differential Equations. An Introductory Text, World Scientific, River Edge, NJ (1994).
2. B. Bojarski, “Old and new on Beltrami equations,” Functional Analytic Methods in Complex Analysis and Applications to Partial Differential Equations: Proc. of the ICTP (February, 8–19, 1988, Trieste, Italy), (1988), pp. 173–187.
3. T. Iwaniec and G. Martin, “What’s new for the Beltrami equation?,” Geometric Analysis and Applications: Proc. Centre Math. Appl. Austral. Nat. Univ. (Canberra, 2000), 39, 132–148 (2001).
4. A. Tungatarov, “Properties of an integral operator in classes of summable functions,” Izv. Akad. Nauk Kazakh. SSR, Ser. Fiz.-Mat., No. 5, 58–62 (1985).
5. F. D. Gakhov, Boundary-Value Problems [in Russian], Nauka, Moscow (1977).