@unpublished{PaneahSchulze1998,
  author    = {Paneah, Boris and Schulze, Bert-Wolfgang},
  title     = {On the existence of smooth solutions of the dirichlet problem for hyperbolic : differential equations},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-25179},
  year      = {1998},
  language  = {en}
}