@article{heterogenouscoefficientsdiscrete,
  title = {Identification of Treatment Effects under Limited Exogenous Variation},
  author = {Whitney K. Newey and Sami Stouli},
  year = {2018},
  eprint = {1811.09837},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/1811.09837v2},
}