@Misc{ 
  DelPis20,
  author = { Della Pietra, Francesco and Piscitelli, Gianpaolo },
  title = { An optimal bound for nonlinear eigenvalues and torsional rigidity on
  domains with holes },
  journal = {  },
  year = { 2020 },
  pages = {  },
  URL = { http://cvgmt.sns.it/paper/5730/ },
  note = { cvgmt preprint}
}