@book{EgorovKondratievSchulze2004,
  author    = {Egorov, Yu. and Kondratiev, V. A. and Schulze, Bert-Wolfgang},
  title     = {On the completeness of root functions of elliptic boundary problems in a domain with conical points on the boundary},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik, Arbeitsgruppe Partiell},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik, Arbeitsgruppe Partiell},
  publisher = {Univ.},
  address   = {Potsdam},
  issn      = {1437-739X},
  pages     = {21 S.},
  year      = {2004},
  language  = {en}
}
@book{EgorovKondratievSchulze2001,
  author    = {Egorov, Yu and Kondratiev, V. A. and Schulze, Bert-Wolfgang},
  title     = {On completeness of eigenfunctions of an elliptic operator on a manifold with concial points},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik, Arbeitsgrupe Partielle Differentialgleichun},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik, Arbeitsgrupe Partielle Differentialgleichun},
  publisher = {Univ.},
  address   = {Potsdam},
  issn      = {1437-339X},
  pages     = {11 S.},
  year      = {2001},
  language  = {en}
}