@Article{ 
  San20a,
  author = { Santilli, Mario },
  title = { Distance functions with dense singular sets },
  journal = { Comm. Partial Differential Equations },
  year = { 2021 },
  doi = { https://doi.org/10.1080/03605302.2021.1871623 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/4757/ },
  note = { cvgmt preprint}
}