@Misc{ 
  CatDamMas20,
  author = { Catino, Giovanni and Dameno, Davide and Mastrolia, Paolo },
  title = { On Riemannian four-manifolds and their twistor spaces: a moving frame approach },
  journal = {  },
  year = { 2020 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4838/ },
  note = { cvgmt preprint}
}