@unpublished{FedosovSchulzeTarkhanov2008,
  author  = {Boris Fedosov and Bert-Wolfgang Schulze and Nikolai Nikolaevich Tarkhanov},
  title   = {A remark on the index of symmetric operators},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(1998) 04},
  year    = {2008},
}