@unpublished{Tarkhanov2009,
  author  = {Nikolai Nikolaevich Tarkhanov},
  title   = {On the root functions of general elliptic boundary value problems},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2005) 07a},
  year    = {2009},
}