@article{defigueiredo_2000,  title={Nonlinear elliptic systems},  volume={72},  ISSN={0001-3765},  url={https://doi.org/10.1590/S0001-37652000000400002},  DOI={10.1590/S0001-37652000000400002},  number={4},  journal={Anais da Academia Brasileira de Ciências},  publisher={Academia Brasileira de Ciências},  author={DEFIGUEIREDO, DJAIRO G.},  year={2000},  month={Dec},  pages={453–469} }