@Article{ 
  GenGorSar16,
  author = { Gentili, Graziano and Gori, Anna and Sarfatti, Giulia },
  title = { A direct approach to quaternionic manifolds },
  journal = { Math. Nachr. },
  year = { 2017 },
  doi = { 10.1002/mana.201500489 },
  volume = { 290 },
  number = { 2-3 },
  pages = { 321-331 },
  URL = { https://gecogedi.dimai.unifi.it/paper/102/ },
  note = { cvgmt preprint}
}