@inproceedings{Pani:20090R,
  author = "Pani, Paolo  and  Cardoso, V.  and  Cadoni, Mariano  and  Cavaglià, Marco",
  title = "{Ergoregion instability rules out black hole doubles}",
  doi = "10.22323/1.075.0027",
  booktitle = "Proceedings of Black Holes in General Relativity and String Theory {\textemdash} PoS(BHs, GR and Strings)",
  year = 2009,
  volume = "075",
  pages = "027"
}