@inproceedings{ijcai2019p782,
  title     = {On Computational Complexity of Pickup-and-Delivery Problems with Precedence Constraints or Time Windows},
  author    = {Tan, Xing and Huang, Jimmy Xiangji},
  booktitle = {Proceedings of the Twenty-Eighth International Joint Conference on
               Artificial Intelligence, {IJCAI-19}},
  publisher = {International Joint Conferences on Artificial Intelligence Organization},
  pages     = {5635--5643},
  year      = {2019},
  month     = {7},
  doi       = {10.24963/ijcai.2019/782},
  url       = {https://doi.org/10.24963/ijcai.2019/782},
}