@Misc{ 
  Vel19,
  author = { Velichkov, Bozhidar },
  title = { Regularity of the one-phase free boundaries },
  journal = { Lecture Notes of the Unione Matematica Italiana, Springer },
  year = { 2023 },
  volume = { 28 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4367/ },
  note = { cvgmt preprint}
}