@inproceedings{KS21,
  author    = {O. Kupferman and S. Sickert},
  title     = {Certifying Inexpressibility},
  booktitle = fossacs21,
  pages = "385-405",
  publisher = {Springer},
  series    = {Lecture Notes in Computer Science},
  volume = "12650",
  year      = {2021}
}