@inproceedings{ijcai2021p614,
  title     = {Policy Learning with Constraints in Model-free Reinforcement Learning: A Survey},
  author    = {Liu, Yongshuai and Halev, Avishai and Liu, Xin},
  booktitle = {Proceedings of the Thirtieth International Joint Conference on
               Artificial Intelligence, {IJCAI-21}},
  publisher = {International Joint Conferences on Artificial Intelligence Organization},
  editor    = {Zhi-Hua Zhou},
  pages     = {4508--4515},
  year      = {2021},
  month     = {8},
  note      = {Survey Track},
  doi       = {10.24963/ijcai.2021/614},
  url       = {https://doi.org/10.24963/ijcai.2021/614},
}