@article{ribeiro_lorena_2006,  title={Lagrangean relaxation bounds for point-feature cartographic label placement problem},  volume={26},  ISSN={0101-7438},  url={https://doi.org/10.1590/S0101-74382006000300002},  DOI={10.1590/S0101-74382006000300002},  number={3},  journal={Pesquisa Operacional},  publisher={Sociedade Brasileira de Pesquisa Operacional},  author={Ribeiro, Glaydston Mattos and Lorena, Luiz Antonio Nogueira},  year={2006},  month={Sep},  pages={459–471} }