Generalized lower and upper approximations in a ring

@article{Yamak2010GeneralizedLA,
  title={Generalized lower and upper approximations in a ring},
  author={Sultan Yamak and Osman Kazanci and Bijan Davvaz},
  journal={Inf. Sci.},
  year={2010},
  volume={180},
  pages={1759-1768}
}