@article{tcs19,
  title = "When are prime formulae characteristic?",
  journal = "Theoretical Computer Science",
  year = "2019",
  volume = "777",
  pages = {3--31},
  issn = "0304-3975",
  doi = {10.1016/j.tcs.2018.12.004},
  author = "Luca Aceto and Della Monica, Dario and
            Ignacio F\'abregas and Anna Ing\'olfsd\'ottir",
  note = "Available online since 6 December 2018"
}