1. Gilbarg, D., Trudinger, N. S., Elliptic Partial Differential Equations of Second Order, Springer-Verlag, New York, 1983.
2. Brézis, H. Anályse Fonctionnelle, Masson Ed., Paris, 1983.
3. Evans, L. C., Partial Differential Equations, Graduate Studies in Mathematics, vol 19, American Mathematical Society, 1998.
4. Adams, R. A., Sobolev Spaces, Academic Press, New York, 1975.
5. McOwen, R., Partial Differential Equations - Methods and Applications, Prentice-Hall, 1996.
6. Rabinowitz, P. H., Minimax Methods in Critical Point Theory with Applications to Differential Equations, CBMS Regional Conference Series in Mathematics, n.65, American Mathematical Society, 1986.
7. Willen, M., Minimax Theorems, Birkhauser, 1996.
8. Struwe, M., Variational Methods - Applications to Nonlinear Partial Differential Equations and Hamiltonian Systems, 2. ed., Springer, 1996.