@unpublished{EgorovKondratievSchulze2008,
  author  = {Yu. Egorov and V. Kondratiev and Bert-Wolfgang Schulze},
  title   = {On completeness of eigenfunctions of an elliptic operator on a manifold with conical points},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2001) 04},
  year    = {2008},
}