@Misc{ 
  Mar21,
  author = { Marconi, Elio },
  title = { Differentiability properties of the flow of 2d autonomous vector fields },
  journal = { Journal of Differential Equations },
  year = { 2021 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/5001/ },
  note = { cvgmt preprint}
}