[1] Antoncev S. N., Kazhikhov A. V., Monakhov V. N.: Boundary Value Problems in Nonhomogeneous Fluid Mechanics. (in russian), Nauka, Novosibirsk, 1983.

[2] Fučík S., Kufner A.: Nonlinear Differential Equations. Elsevier Scientifìc Publishing Company, Amsterdam-Oxford-New York, 1980. MR 0558764