@article{JMLR:v27:24-1990,
  author  = {Xichen Guo and Zheng Li and Biwei Huang and Yan Zeng and Zhi Geng and Feng Xie},
  title   = {Testability of Instrumental Variables in Additive Nonlinear, Non-Constant Effects Models},
  journal = {Journal of Machine Learning Research},
  year    = {2026},
  volume  = {27},
  number  = {154},
  pages   = {1--60},
  url     = {http://jmlr.org/papers/v27/24-1990.html}
}