@unpublished{EgorovKondratievSchulze2008,
  author  = {Jurij V. Egorov and V. A. Kondratiev and Bert-Wolfgang Schulze},
  title   = {On the completeness of root functions of elliptic boundary problems in a domain with conical points on the boundary},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2004) 17},
  year    = {2008},
}