@article{Usoskin:201785,
  author = "Usoskin, Ilya  and  Asvestari, Eleanna  and  Willamo, Teemu  and  Gil, Agnieszka  and  Kovaltsov, Gennady  and  Mikhailov, Vladimir  and  Mayorov, Andrey",
  title = "{Analysis of Ground-Level Enhancements: Strong events are hard}",
  doi = "10.22323/1.301.0126",
  journal = "PoS",
  year = 2017,
  volume = "ICRC2017",
  pages = "126"
}